[255]*255Opinion
PANELLI, J.
We granted review to decide whether Education Code section 39807.5,1 which authorizes school districts to charge fees for pupil transportation, violates either the free school guarantee (art. IX, § 5) or the equal protection clause (art. I, § 7, subd. (a)) of the California Constitution. We conclude that the statute, on its face, violates neither constitutional guarantee.2
Facts
This case has its roots in an earlier case. In 1985, Francisco Salazar (the intervener in the present case) filed a taxpayers’ suit in Ventura County Superior Court against the State Department of Education, the State Board of Education, the Superintendent of Public Instruction, and the Fillmore Unified School District,3 alleging that defendants’ implementation of section 39807.5 violated the free school guarantee and the equal protection clause of the California Constitution.4 The superior court ruled that the school districts that assessed the fees were indispensable parties but did not reach the merits. The Court of Appeal, Second District, Division Six, reversed, holding that the districts were not indispensable parties, and that section 39807.5 violated both the free school guarantee and the equal protection clause of the state [256]*256Constitution. (Salazar v. Honig (May 10, 1988) Cal.App. B026629.) On September 1, 1988, we denied review but ordered the Court of Appeal opinion depublished. On remand, the superior court entered judgment against the defendants.
Pursuant to the superior court’s order, the State Department of Education (Department) issued a legal advisory, informing all school districts that section 39807.5 was unconstitutional and directing them to cease charging for transportation. However, numerous school districts, which were not parties to the Ventura County action, did not follow the advisory, taking the position that the statute was not unconstitutional.
The present action was instituted to determine the validity of section 39807.5. Twenty-five school districts as plaintiffs and the Department as defendant agreed to submit to the Sacramento County Superior Court on a stipulated statement of facts for judgment “to determine the rights of the parties.” (Code Civ. Proc., § 1138.) Eighteen of the school districts had continued to charge for transportation, while seven had ceased after the decision in Salazar v. Honig, supra, Cal.App.) and the Department’s legal advisory. The purpose of the action was to determine the facial validity of the statute, rather than to litigate the propriety of any particular application.
Salazar successfully moved to intervene. He also moved to dismiss, alleging that the Department was bound by the judgment in the Ventura County action as a party and that the school districts were bound as agents of the Department. The trial court denied the motion to dismiss and granted judgment for the Department, ruling that section 39807.5 facially violated the free school guarantee. (Cal. Const., art. IX, § 5.)
The Court of Appeal, Third District, in a unanimous decision, reversed. The court held that the districts were not collaterally estopped to maintain the action, because the public interest exception to the rule of collateral estoppel applied; the court therefore did not consider whether the districts were agents of the Department or in privity with it. The court also held that section 39807.5 on its face violates neither the free school guarantee nor the equal protection clause of the California Constitution.
Collateral Estoppel
As a threshold matter, we must determine whether the Court of Appeal was correct in holding that this action is not barred by the earlier judgment in Salazar v. Honig (supra, Cal.App.).
Salazar contends that the Department is bound by the judgment in Salazar v. Honig (supra, Cal.App.), and that the school districts are also [257]*257bound, since they are agents of the Department and in privity with it. “Generally, collateral estoppel bars the party to a prior action, or one in privity with him, from relitigating issues finally decided against him in the earlier action.” (City of Sacramento v. State of California (1990) 50 Cal.3d 51, 64 [266 Cal.Rptr. 139, 785 P.2d 522], citing Clemmer v. Harford Insurance Co. (1978) 22 Cal.3d 865, 874 [151 Cal.Rptr. 285, 587 P.2d 1098] (City of Sacramento).) Salazar also claims that it was inappropriate for the Sacramento County Superior Court to take jurisdiction over the action when the state defendants were bound by the injunctions issued as a result of the Ventura County action. The Department and the school districts, on the other hand, maintain that the requirements of collateral estoppel are not met as to the school boards, because the boards are neither agents of, nor in privity with, the Department. Moreover, they maintain, even if the formal requirements are met, the Court of Appeal was correct in its holding that the action was not barred, because the requirements of the public interest exception to the doctrine of collateral estoppel are met, and we agree.
As we will discuss, it appears that the Court of Appeal properly applied the public interest exception. Therefore, like the Court of Appeal, we need not consider whether the districts were agents of the Department or in privity with it. We would be reluctant to do so in the absence of a factual record when our decision might have unforeseeable consequences in other cases and there is an alternative basis for our conclusion.
We recently affirmed the rule that, “ ‘when the issue is a question of law rather than of fact, the prior determination is not conclusive either if injustice would result or if the public interest requires that relitigation not be foreclosed. [Citations.]’ ” (City of Sacramento, supra, 50 Cal.3d atp. 64, quoting Consumers Lobby Against Monopolies v. Public Utilities Com. (1979) 25 Cal.3d 891, 902 [160 Cal.Rptr. 124, 603 P.2d 41].) The issue in City of Sacramento was whether local governments were entitled to subvention of the costs of extended mandatory unemployment insurance coverage. We determined that the state should not be bound by a prior judgment on the issue because “the consequences of any error transcend those which would apply to mere private parties”; any error would also affect the taxpayers and employers of the state. (City of Sacramento, supra, 50 Cal.3d at pp. 64-65.)
It would be equally detrimental to the public interest to apply collateral estoppel here. Because Salazar v. Honig (supra, Cal.App.) was ordered not to be officially published and may not be cited as legal authority, there has been a continuing and demonstrable uncertainty about the validity of section 39807.5. School districts do not know if they can constitutionally charge for [258]*258school transportation, and have responded to this uncertainty in different ways. It is clearly in the public interest that school districts have a uniform understanding of this important issue. If we were to hold that this action could not go forward, and if Salazar v. Honig was wrongly decided, school districts would be unable to charge fees for transportation, and so they would be unable to collect those revenues, to which they are entitled by statute. Students might also be adversely affected, because those districts that could not afford to fund bus transportation out of their limited revenues might be forced to eliminate the service. The public interest, especially the interests of school districts, taxpayers, and students, will best be served by a final resolution by this court of whether the fees are permissible.
In addition, the unusual history of Salazar v. Honig (supra, Cal.App.) suggests that it would be in the public interest to permit this action to go forward. Although Salazar presented evidence at that trial on the unconstitutionality of section 39807.5, the state defendants did not present any evidence on the issue, nor did they argue that the statute was constitutional. Their defense was based solely on the contention that the school districts were indispensable parties. Thus, no one during the Salazar v. Honig proceedings contended that the statute could be applied in a manner consistent with the Constitution. The public interest would best be served by a determination of this important issue based on the presentation of both sides of the controversy.
The practical result of Salazar’s position would be that the constitutionality of section 39807.5 would never again be litigated. If, as Salazar contends, all of the school districts in the state of California are bound by the decision in Salazar v. Honig (supra, Cal.App.) then no school district is free either to charge a fee for home-to-school transportation or to assert the constitutionality of the statute. In that case, there would be no opportunity for anyone ever to challenge the legal grounds of the unpublished ruling. Thus, in one fell swoop, by binding all the parties in the state who have any interest in the issue without naming them as parties to the first action, Salazar would have effectively prevented the constitutionality of this legislative enactment from ever being fully tested or defended.
None of the cases Salazar relies on convinces us that the Court of Appeal erred in applying the public interest exception. Salazar points out that the injustice exception to the rule of collateral estoppel has been criticized; however, that exception is distinct from the public interest exception, on which the Court of Appeal relied. (See Slater v. Blackwood (1975) 15 Cal.3d 791, 796 [126 Cal.Rptr. 225, 543 P.2d 593], criticizing Greenfield v. Mather [259]*259(1948) 32 Cal.2d 23, 35 [194 P.2d 1].) Salazar also brings to our attention cases concerning injunctive orders or class actions, in which parties were held to be bound by an earlier judgment. (See Ross v. Superior Court (1977) 19 Cal.3d 899 [141 Cal.Rptr. 133, 569 P.2d 727], and Cartwright v. Swoap (1974) 40 Cal.App.3d 567 [115 Cal.Rptr. 402].) He suggests that if we were to allow cases such as this to go forward, the result would be a “judicial administration nightmare.” However, the cases he relies on do not address the particular exception that the Court of Appeal applied.
The public interest exception is an extremely narrow one; we emphasize that it is the exception, not the rule, and is only to be applied in exceptional circumstances. However, the unusually compelling facts in this case make it appropriate for us to apply the exception here. The matter before us involves a pure question of law. It affects the public in general, including children, parents and taxpayers; it also affects the ability of school districts to provide and finance school transportation. Because the school districts were not parties to the earlier case of Salazar v. Honig (supra, Cal.App.) they have not had the opportunity to litigate the constitutionality of section 39807.5. If the action were barred from going forward, then the state of the law on a matter of statewide importance would remain permanently unclear and unsettled. Therefore, we conclude that the Court of Appeal did not err in applying the public interest exception to the rule of collateral estoppel, and that the parties were not barred from pursuing their case in the Sacramento County Superior Court.5
Free School Guarantee
Salazar argues that section 39807.5 violates California’s free school guarantee, which provides that “[t]he Legislature shall provide for a system [260]*260of common schools by which a free school shall be kept up and supported in each district at least six months in every year, after the first year in which a school has been established.” (Cal. Const., art. IX, § 5.)6 We must first establish the scope of our inquiry. The statute is a legislative enactment. “In considering the constitutionality of a legislative act we presume its validity, resolving all doubts in favor of the Act. Unless conflict with a provision of the state or federal Constitution is clear and unquestionable, we must uphold the Act. [Citations.] Thus, wherever possible, we will interpret a statute as consistent with applicable constitutional provisions, seeking to harmonize Constitution and statute. [Citations.]” (California Housing Finance Agency v. Elliott (1976) 17 Cal.3d 575, 594 [131 Cal.Rptr. 361, 551 P.2d 1193].)7
The. first step in interpreting an ambiguous constitutional provision is to look at the intent of the framers. (See Story v. Richardson (1921) 186 Cal. 162, 165 [198 P. 1057, 18 A.L.R. 750].) The California free school guarantee was adopted during the 1878-1879 Constitutional Convention. It substantially followed a provision of the state’s 1849 Constitution, but, unlike the earlier provision, it required schools to be “free.” (See Debates & Proceedings, Cal. Const. Convention 1878-1879, p. 1100, remarks of Mr. Winans.) The history of the 1878-1879 constitutional debates gives very little guidance on the meaning of the term “free school,” except to note that “[a] free school is a school at which pupils may attend without charge.” (Debates & Proceedings, Cal. Const. Convention 1878-1879, supra, at p. 1100, remarks of Mr. Jones.) The only evidence we have located of whether the framers expected schools to provide transportation is the statement of one delegate that he knew “many a small common school, or district, where children ride on horseback a distance of five or eight miles to school in the morning, and home at night.” (Ibid.) This statement suggests that although the framers were aware of the difficulties students might face in getting to school, they did not consider transportation part of the school system. Thus, although the history of the 1879 Constitution does not make entirely clear whether the framers would have intended to allow school districts to charge a fee for transportation if they chose to provide that service, it supports the view that transportation is not included within the free school guarantee.
In the absence of more explicit guidance on the intent of the framers, the next step is to look to our previous cases to shed light on the meaning of the [261]*261free school guarantee. In the past, we have supplemented our own history of interpreting the free school guarantee by looking to other states’ interpretations of similar provisions in their states’ constitutions. (See Hartzell v. Connell, supra, 35 Cal.3d 899, 905-912.) It is especially appropriate for us to continue to do so in this case, because California’s provisions for schooling appear to have been at least partially modeled on similar provisions in other states’ constitutions. (See Debates, Cal. Const. Convention 1849, p. 206 [former art. IX, § 3, predecessor to current art. IX, § 5, similar to provisions adopted by several other states]; see also Debates & Proceedings, Cal. Const. Convention 1878-1879, supra, at p. 1087 [proposed art. IX, § 1 taken partly from Arkansas and Missouri Constitutions, and proposed art. IX, § 4 taken from the Illinois Constitution] and p. 1089 [spread of free school guarantees from Missouri].)
The leading case interpreting California’s free school provision is Hartzell v. Connell, supra, 35 Cal.3d 899 (Hartzell). Hartzell involved a challenge to the fees a school district charged for participation in such extracurricular activities as dramatic productions, music groups, and cheerleading groups. As previously noted, there was no statutory authorization for such fees. We held that the free school guarantee extends not only to classes, but also to extracurricular activities which are “ ‘educational’ in character.” (Hartzell, supra, 35 Cal.3d at p. 911.) However, Salazar asks us to hold that the guarantee includes transportation to and from school, which none of the educator parties maintain is an educational activity.8
Salazar asserts that school-provided transportation, although not educational in character, is nonetheless covered by Hartzells understanding of the free school guarantee because it is an “integral fundamental part of [] elementary and secondary education," or a “necessary element[] of any school’s activity.” (Id. at p. 905, citing Bond v. Ann Arbor School District (1970) 383 Mich. 693, 702 [178 N.W.2d 484, 41 A.L.R.3d 742].)
In attempting to determine whether the extracurricular activities in Hartzell came within the protection of the free school guarantee, we considered two approaches to resolution of the issue used by other states with similar constitutional provisions. The first approach, which we rejected, restricts the free school guarantee to “programs that are ‘essential to the prescribed curriculum.’ [Citations.]” (Hartzell, supra, 35 Cal.3d at p. 905.) This approach would not have guaranteed free access to activities that are not [262]*262contained within a school’s regular academic coursework. The second approach extends the free school guarantee “to all activities which constitute an ‘integral fundamental part of the elementary and secondary education’ or which amount to "’necessary elements of any school’s activity.” ’ [Citations.]” (Ibid.) This second approach, we noted, had led states that adopted it to strike down extracurricular activity fees as violative of their free school provisions. (Id. at pp. 905-906.) After reviewing the history and purpose of California’s free school guarantee, we approved the second, broader approach, because it “does not sever the concept of education from its purposes. It focuses not upon the formalities of credit, but upon the educational character of the activities in question.” (Id. at p. 909, italics added.)
Applying this second approach in Hartzell, we noted that the activities in question served the purposes of education: to prepare students for participation in political affairs and in institutional structures such as labor unions and business enterprises and to serve as a “unifying social force.” (Hartzell, supra, 35 Cal.3d at pp. 907-908.) We determined that extracurricular activities constitute “an integral component of public education” and are “a fundamental ingredient of the educational process.” We also noted that extracurricular activities are “[no] less fitted for the ultimate purpose of our public schools, to wit, the making of good citizens physically, mentally, and morally, than the study of algebra and Latin . . . .” (Id. at p. 909, internal quotation marks and citations omitted.) We therefore concluded that, “[s\ince it is not disputed that the programs involved in this case are ‘educational’ in character, they fall within [the free school] guarantee.” (Id., at p. 911, italics, added.)
It is clear that we adopted the second of the two approaches, in which we looked at whether an activity is an integral, fundamental part of education or a necessary element of any school’s activity, specifically because that approach focuses “upon the educational character of the activities in question.” (Hartzell, supra, 35 Cal.3d at p. 909, italics added.) The two parts of the approach we adopted both focus on whether an activity is educational in character. (“The second approach . . . focuses not upon the formalities of credit, but upon the educational character of the activities in question.” (Ibid.)) As a result, we twice stated our holding that “all educational activities . . . offered to students by school districts fall within the free school guarantee” (id. at p. 911, italics added), and that ‘the imposition of fees for educational activities offered by public high school districts violates the free school guarantee.” (Id., at p. 913, italics added.) Thus, neither our holding nor our reasoning in Hartzell leads to the conclusion that noneducational activities are protected by the free school guarantee. Although in Hartzell we [263]*263adopted a broad understanding of what activities are protected as educational, we did not extend that expansive understanding of the free school clause beyond the realm of educational activities to noneducational supplemental services. Transportation is simply not an educational activity. It is not protected by the reasoning of Hartzell.
Against this conclusion, Salazar contends that, although bus transportation is not educational, it is a ‘““necessary element[] of any school’s activity.” ’ ” (Hartzell, supra, 35 Cal.3d at p. 905.) However, it appears that Salazar has misunderstood what the cases mean by the quoted language. We believe that the Court of Appeal in this case was correct when it concluded that transportation is not an essential element of school activity.
The language we adopted in Hartzell was derived from Bond v. Ann Arbor School District (supra, 383 Mich. 693 [178 N.W.2d at p. 487]), which held that, under the Michigan free school guarantee, schools could not charge a fee for textbooks and school supplies. Quoting Paulson v. Minidoka County School District No. 331 (1970) 93 Idaho 469 [463 P.2d 935, 938-939], the Michigan Supreme Court stated that “ ‘[t]extbooks are necessary elements of any school’s activity. They represent a fixed expense peculiar to education, the benefits from which inure to every student in equal proportion . . . solely as a function of his being a student. Unlike pencils and paper, the student has no choice in the quality or quantity of textbooks he will use if he is to earn his education. He will use exactly the books, prescribed by the school authorities, that his classmates use; and no voluntary act of his can obviate the need for books nor lessen their expense. School books are, thus, indistinguishable from other fixed educational expense items such as school building maintenance or teachers’ salaries.’ ” (Bond, supra, 178 N.W.2d at p. 487.) Thus, the court concluded, textbooks and school supplies were “necessary elements of any school’s activity,” and must be provided without cost to the students. (Id. at p. 488.)9
None of these considerations apply to school bus transportation. Students are not required to use the same means of transportation as their classmates [264]*264in order to get to school to receive an education; individual students may choose different modes of transportation to suit their own circumstances. Unlike textbooks or teachers’ salaries, transportation is not an expense peculiar to education. Without doubt, school-provided transportation may enhance or be useful to school activity, but it is not a necessary element which each student must utilize or be denied the opportunity to receive an education.10
This conclusion is especially true in this state, since, as the Court of Appeal correctly noted, school districts are permitted, but not required, to provide bus transportation. (§ 39800.) If they choose, districts may dispense with bus transportation entirely and require students to make their own way to school.11 Bus transportation is a service which districts may provide at their option, but schools obviously can function without it. Therefore, we are not persuaded by Salazar’s argument that, although bus transportation is not an educational activity, it is protected by the free school guarantee as a “necessary element of any school’s activity.”
Our conclusion appears to be in accord with the authority in other states with similar free school guarantees. Courts that have considered the issue have arrived at the conclusion that states or school districts may charge a fee for bus transportation without violating the free school guarantee. A Michigan court relied on Bond v. Ann Arbor School District, supra, for its conclusion that transportation was not an essential part of a system of free public schools in the way that books and school supplies were. (Sutton v. Cadillac Area Public Schools (1982) 117 Mich. App. 38 [323 N.W.2d 582, 583-584], citing Bond, supra, 383 Mich. 693 [178 N.W.2d 484].) Citing Sutton, the North Dakota Supreme Court held in Kadrmas v. Dickinson Public Schools [265]*265(N.D. 1987) 402 N.W.2d 897, affirmed (1988) 487 U.S. 450,12 that districts could charge for bus transportation consistent with the state constitutional article mandating a uniform system of free public schools. (N.D. Const., art. VIII, § 2.) In reaching its holding, the court stated that “transportation is not a necessary element of the educational process, and it is not an integral part of the educational system to which the constitution refers in requiring the Legislature to provide ‘a uniform system of free public schools.’ Although transportation may be an important prerequisite to accepting the educational opportunities offered in the public school system it is not part of the system.” (402 N.W.2d at p. 901.) The court stated that, as with other important prerequisites to education, such as good nutrition and proper immunizations, a state may participate in providing them, but was not required to do so. (Id. at pp. 901-902.) We find this analysis to be reasonable and persuasive. Thus, a line of cases following Bond, on which we relied in Hartzell, supra, 35 Cal.3d 899, to conclude that the free school guarantee covers extracurricular activities, supports our conclusion that states may charge a fee for transportation consistent with the free school guarantee.
Finally, Salazar contends that section 39807.5 should be held invalid because of the “stigma” attached to applying for a waiver. (See Hartzell, supra, 35 Cal.3d at p. 912.) Salazar’s argument ignores the crucial fact that Hartzell involved a fee for activities that were protected by the free school guarantee; we based our rejection of the waiver on the requirement that educational extracurricular activities be truly free. In this case, the fee in question is for a noneducational service. There is no more stigma attached to applying for a transportation waiver than there is in applying for any other noneducational government benefit, such as subsidized school lunches. (See § 49550 et seq.)
As noted earlier, section 39807.5 is a legislative enactment; it is our duty to uphold it unless its unconstitutionality is clear and unquestionable. (California Housing Finance Agency v. Elliott, supra, 17 Cal.3d 575, 594; accord, Dean v. Kuchel (1951) 37 Cal.2d 97, 101 [230 P.2d 811].) Based on the foregoing analysis, we cannot conclude that it is clear and unquestionable that the statute, on its face, violates the free school guarantee. Therefore, we hold that section 39807.5 does not violate California’s free school guarantee.
[266]*266Equal Protection
Salazar also argues that section 39807.5 violates California’s equal protection clause. (Cal. Const., art. I, § 7, subcl. (a).)13 He claims that the statute discriminates against poor students and that it creates a classification based on wealth that will affect children’s ability to exercise their fundamental right to education. (See Serrano v. Priest (1971) 5 Cal.3d 584, 604-610 [96 Cal.Rptr. 601 [487 P.2d 1241, 41 A.L.R.3d 1187] (Serrano I), and Serrano v. Priest (1976) 18 Cal.3d 728, 765-766 [135 Cal.Rptr. 345, 557 P.2d 929], cert. den. 432 U.S. 907 [53 L.Ed.2d 1079, 97 S.Ct. 2951] (Serrano II).) Therefore, Salazar contends, we should subject the statute to strict scrutiny rather than to rational basis analysis.
Salazar’s claims that school transportation fees discriminate against the poor and burden the exercise of a fundamental right might have merit if the statute were to be applied in such a way that children were prevented from attending school because they could not afford to pay the fees. However, section 39807.5 specifically provides that indigent children must be exempted from paying fees for transportation. If the statute is properly administered, no child will be denied transportation to school because of poverty. We have no reason to believe, in this facial challenge, that the statute will be applied improperly.
[267]*267Salazar also contends that section 39807.5 allows impermissible disparity of treatment among students in different districts, based on whether or not each district charges for transportation and how each defines indigency. (See Serrano II, supra, 18 Cal.3d at pp. 761, 765-766.) However, this need not result in an equal protection violation. Under our interpretation of the statute, a student who cannot afford to pay for transportation to attend school may not be charged for school-provided transportation. If a district provides transportation without charge, the service will be free to all students; if a district charges for transportation, students who cannot afford to pay the fee will be exempted. Therefore, poor students in different districts will have equal access to school-provided transportation, if their districts elect to provide it.14
Because this is a challenge to the facial validity of section 39807.5, our task is to determine whether the statute can constitutionally be applied. “To support a determination of facial unconstitutionality, voiding the statute as a whole, petitioners cannot prevail by suggesting that in some future hypothetical situation constitutional problems may possibly arise as to the particular application of the statute .... Rather, petitioners must demonstrate that the act’s provisions inevitably pose a present total and fatal conflict with applicable constitutional prohibitions.” (Pacific Legal Foundation v. Brown (1981) 29 Cal.3d 168, 180-181 [172 Cal.Rptr. 487, 624 P.2d 1215], italics in original.) In this case, there is no evidence that the statute has been or will be applied in such a way as to discriminate against poor students or affect their ability to obtain an education. Therefore, we conclude that the Court of Appeal was correct in holding that the statute does not facially violate equal protection.
Conclusion
For the foregoing reasons, we conclude that, on its face, section 39807.5 does not violate California’s free school guarantee or equal protection clause. Therefore, the judgment of the Court of Appeal is affirmed.
Lucas, C. J., Kennard, J., Arabian, J., Baxter, J., and George, J., concurred.