Greaney, J.
The plaintiffs, public school students in the high school class of 2003, challenge the facial validity of 603 Code Mass. Regs. § 30.03 (2000), a regulation adopted by the Board of Education (board), which required them to pass the tenth grade English language arts and mathematics sections of the Massachusetts Comprehensive Assessment System examination (MCAS exam) in order to graduate from high school.4 The plaintiffs sought a preliminary injunction enjoining the defendants from enforcing the regulation and from requiring [754]*754students in the high school class of 2003 to pass the tenth grade English language arts and mathematics sections of the MCAS exam as a prerequisite to the award of a high school diploma. A judge of the Superior Court denied the preliminary injunction, and the plaintiffs appealed. We granted the plaintiffs’ application for direct appellate review and now affirm the judge’s order.
1. The background of the case is as follows. In McDuffy v. Secretary of the Executive Office of Educ., 415 Mass. 545, 617-619 (1993), this court held that the Massachusetts Constitution imposes an enforceable duty on the Commonwealth to ensure that all children in its public schools receive an education that is to include certain specific training.5 6Virtually simultaneously with the June 15 release of the McDuffy decision, the Legislature by emergency preamble, on June 18, 1993, enacted the Education Reform Act of 1993 (Act), St. 1993, c. 71. Section 27 of the Act, which rewrote G. L. c. 69, § 1, sets forth its intent and purpose in the following terms:
“It is hereby declared to be a paramount goal of the [Cjommonwealth to provide a public education system of sufficient quality to extend to all children
St. 1993, c. 71, § 27.
Of relevance are three sections of G. L. c. 69, namely, §§ ID, IE, and II, which were inserted by St. 1993, c. 71, § 29. These provisions imposed various obligations on the commissioner and the board, in furtherance of education reform, including obligations to develop “academic standards” and “curriculum frameworks” in certain “core subjects.” See G. L. c. 69, § ID, IE. First, the board, through the commissioner, was required “to institute a process to develop academic standards for the core subjects of mathematics, science and technology, history and social science, English, foreign languages and the arts.”7 Id. at § ID, second par. Second, the board was required to direct the commissioner “to institute a process for drawing up curriculum frameworks for the core subjects covered by the academic standards provided in [§ ID].” Id. at § IE, first par. [756]*756The curriculum frameworks “shall present broad pedagogical approaches and strategies for assisting students in the development of the skills, competencies and knowledge called for by these standards. . . . They shall provide sufficient detail to guide the promulgation of student assessment instruments.” Id.
The Act imposed on the board an obligation to create objective “assessments” to measure both school and student performance. See G. L. c. 69, § II, first, second, and third pars., inserted by St. 1993, c. 71, § 29.8 The first three paragraphs of § II, provide, in pertinent part:
“The board shall adopt a system for evaluating on an annual basis the performance of both public school districts and individual public schools. With respect to individual schools, the system shall include instruments designed to assess the extent to which schools and districts succeed in improving or fail to improve student performance, as defined by student acquisition of the skills, competencies and knowledge called for by the academic standards and embodied in the curriculum frameworks established by the board pursuant to [§§ ID and IE] in the areas of mathematics, science and technology, history and social science, English, foreign languages and the arts, as well as by other gouges of student learning judged by the board to be relevant and meaningful to students, parents, teachers, administrators, and taxpayers.
“The system shall be designed both to measure outcomes and results regarding student performance, and to improve the effectiveness of curriculum and instruction. In its design and application, the system shall strike a balance among considerations of accuracy, fairness, expense and administration. The system shall employ a variety of assessment instruments on either a comprehensive or statistically valid sampling basis. Such instruments shall be criterion referenced, assessing whether students are meeting the academic standards described in this chapter. As much as is practicable, especially in the case of students whose performance is difficult to assess using [757]*757conventional methods, such instruments shall include consideration of work samples, projects and portfolios, and shall facilitate authentic and direct gouges of student performance. Such instruments shall provide the means to compare student performance among the various school systems and communities in the [Cjommonwealth, and between students in other [Sjtates and in other nations, especially those nations which compete with the [Cjommonwealth for employment and economic opportunities. . . .
“In addition, comprehensive diagnostic assessment of individual students shall be conducted at least in the fourth, eighth and tenth grades. Said diagnostic assessments shall identify academic achievement levels of all students in order to inform teachers, parents, administrators and the students themselves, as to individual academic performance. The board shall develop procedures for updating, improving or refining the assessment system.” (Emphases added.)
The Act also amended G. L. c. 69 to impose a graduation requirement called the “competency determination.” G. L. c. 69, § ID, inserted by St. 1993, c. 71, § 29. The provision reads, in pertinent part:
“The ‘competency determination’ shall be based on the academic standards and curriculum frameworks for tenth graders in the areas of mathematics, science and technology, history and social science, and English,[9] and shall represent a determination that a particular student has demonstrated mastery of a common core of skills, competencies and knowledge in these areas, as measured by the assessment instruments described in [§ 1 ]. Satisfaction of the requirements of the competency determination shall be a condition for high school graduation. If the particular student’s assessment results for the tenth grade do not demonstrate the required level of competency, the student shall have the right to participate in the assessment program for the following year or years. Students who fail to satisfy the requirements of the competency determina[758]*758tian may be eligible to receive an educational assistance plan designed within the confines of the foundation budget to impart the skills, competencies and knowledge required to attain the required level of mastery. ...” (Emphasis added.)
Id. at § ID, fourth par., (i).10 All high school students attending public schools, including vocational high schools and charter schools, and all students educated with State funds, are subject to the competency determination.
The Act granted extensive authority to the board:
“The board shall establish such other policies as it deems necessary to fulfill the purposes of this chapter.... In accordance with the provisions of [G. L. c. 30A], the board may promulgate regulations as necessary to fulfill said purposes. Said regulations shall be promulgated so as to encourage innovation, flexibility and accountability in schools and school districts.”
G. L. c. 69, § IB, twenty-fourth par., inserted by St. 1993, c. 71, § 29.
The board undertook its mandate to implement the Act and, over time, established curriculum frameworks for all core subjects and formulated the MCAS exam. The exam is a customized test, designed by a national testing company specifically for Massachusetts to be closely aligned with the curriculum frameworks. The MCAS exam contains multiple-choice questions; short answer questions requiring responses ranging from a number or a few words to several sentences; open response questions, requiring students to write a detailed or descriptive answer up to one-half page long, or a chart or graph; and writing prompts, requiring students to write a composition that develops an idea coherently and uses proper punctuation, spelling, and grammar. There are four levels of “performance levels,” or scores, for the MCAS exam. A scaled score of 200-219 corresponds to “failing,” a scaled score of 220-238 corresponds to “needs improvement,” a scaled score of 240-258 [759]*759corresponds to “proficient,” and a scaled score of 260-280 corresponds to “advanced.”
The MCAS exam was administered for the first time in May, 1998, and initially covered the core subjects of English language arts, mathematics, and science and technology. On May 1, 1998, the department publicly announced that the MCAS exam in four subjects — English, mathematics, science, and social studies — would be used as the high school competency determination, or graduation requirement, called for in G. L. c. 69, § ID, to begin with students enrolled in the tenth grade in 2001, who would be graduating in 2003.
In 1998, forty-two per cent of eighth graders taking the MCAS exam failed the mathematics section, fourteen per cent failed the English section, and forty-one per cent failed the science and technology section. The same year, fifty-two per cent of tenth graders failed the mathematics section, twenty-eight per cent failed the English section, and thirty-six per cent failed the science and technology section. In 1999, forty per cent of eighth graders taking the MCAS exam failed the mathematics section, thirteen per cent failed the English section, forty-five per cent failed the science and technology section, and forty-nine per cent failed a newly added history section. That same year, fifty-three per cent of tenth graders failed the mathematics section, thirty-two per cent failed the English section, and thirty-eight per cent failed the science and technology section. Tenth grade students were not tested in history. Board minutes indicated that, at least in part because of those results, the board, in 1999, began to discuss the possibility of phasing various core subjects into the MCAS exam graduation requirement. The board adopted the challenged regulation, 603 Code Mass. Regs. § 30.03, on January 25, 2000, and the regulation became effective on February 18, 2000. The regulation provides:
“Students in the graduating class of 2003 shall meet or exceed the Needs Improvement threshold scaled score of 220 on both the English Language Arts and the Mathematics MCAS grade 10 tests in order to satisfy the requirements of the Competency Determination. The Board [760]*760intends to raise the threshold scaled score required for the Competency Determination in future years.”11
The board also adopted a regulation, 603 Code Mass. Regs. § 30.05, that creates an alternate way for students to satisfy the graduation requirement. The regulation establishes a “performance appeals” process that allows a student to satisfy the MCAS grade ten exam requirement despite a nonpassing score. 603 Code Mass. Regs. § 30.05(1), (10). The regulation contains several waivable eligibility requirements, including scoring at least a score of 216 on a prior MCAS exam. Id. at § 30.05(3)(b), (4). No performance appeal can be brought for a student whose knowledge in English language arts and mathematics does not at least meet “a performance level equivalent to 220 on the MCAS grade 10 test required for the [competency [determination.”12 Id. at § 30.05(1).
Approximately six months after the board promulgated the regulation, the Legislature, by St. 2000, c. 159, § 137, amended § II of G. L. c. 69 to require certain school districts to prepare “MCAS success plans.” Section II provides that:
“Each school district in which more than [twenty] per cent of the students score below level two [i.e., needs improvement] on the [MCAS] exam. . . shall submit an MCAS success plan to the department. The plan shall describe the school district’s strategies for helping each student to master the skills, competencies and knowledge [761]*761required for the competency determination described in [§ ID, fourth par., (i)].”
The Legislature has also specifically made reference to the MCAS exam in numerous budget line items. The Legislature appropriated funds in the fiscal year (FY) 2003 budget for intensive education programs to assist students in passing the MCAS exam. See St. 2002, c. 184, § 2, line item 7061-9404. Additional funds were appropriated in the FY 2004 budget, some directed toward helping students “in the graduating classes of 2003, 2004, and 2005 who have not obtained a competency determination on either the tenth grade English or math MCAS exams.” See St. 2003, c. 26, § 2, line item 7061-9404. Both branches of the Legislature also rejected amendments to the FY 2004 budget that would have eliminated the MCAS graduation requirement for students in the classes of 2003 and 2004. See 2003 House J. 261; 2003 Senate J. 242-243.
By March, 2003, approximately ninety per cent of the members of the high school graduation class of 2003 had passed the tenth grade English and math MCAS exams, making them eligible for high school graduation, compared to only sixty-eight per cent when the class first took the exam in 2001. High school juniors and seniors who, as of March, 2003, had not yet passed were given an opportunity to participate in intensive English and mathematics remedial programs, and were permitted to take the MCAS exam again in May, 2003, in time for graduation in June. Students who failed the May, 2003, MCAS exam were given the opportunity to attend free remediation classes during the summer and to take the exam again in August, 2003. Also, the board and the department worked to develop remedial education programs in community colleges and workplace settings for students who satisfied local graduation requirements but had not yet obtained the competency determination. These students have been permitted, at no cost, to take further MCAS exams as many times as they choose. The board has established a “certificate of attainment” that school committees may award to students who meet local high school graduation requirements, but who do not qualify for a diploma because they have not passed the English language arts or mathematics sections of the MCAS exam.
[762]*762The plaintiffs are members of the high school class of 2003. With one exception, the plaintiffs are public school students. One plaintiff, who is blind, is enrolled at public expense at the Perkins State School for the Blind. Some of the plaintiffs have one or more disabilities and have received special education services. One student has limited English proficiency. All of the plaintiffs have satisfied local graduation requirements, and would have graduated but for their failure to pass either or both the English language arts and mathematics sections of the MCAS exam. Several of the plaintiffs have failed multiple administrations of the mathematics section of the MCAS exam. One plaintiff, on four occasions, has failed both the English language arts and mathematics sections of the MCAS exam, despite his participation in remediation programs. This plaintiff was told that his cohort (class size) was too small to permit a performance appeal.
2. The judge applied the established test in assessing the plaintiffs’ application for a preliminary injunction, see Tri-Nel Mgt., Inc. v. Board of Health of Barnstable, 433 Mass. 217, 219 (2001), and she kept in mind the additional requirement that, when a party seeks to enjoin governmental action, the judge must also consider whether the grant of an injunction would adversely affect the public interest. See Landry v. Attorney Gen., 429 Mass. 336, 343 (1999), cert, denied, 528 U.S. 1073 (2000). The judge also correctly recognized that the significant remedy of a preliminary injunction should not be granted unless the plaintiffs had made a clear showing of entitlement thereto. Id.
The plaintiffs argue essentially that the regulation is facially invalid because it operates ultra vires in conflict with several provisions of the Act. In challenging the regulation, the plaintiffs have the burden, a formidable one, of demonstrating its illegality. See Massachusetts Fed’n of Teachers v. Board of Educ., 436 Mass. 763, 771 (2002); Greenleaf Fin. Co. v. Small Loans Regulatory Bd., 377 Mass. 282, 293 (1979). An administrative agency, like the board, has considerable leeway in interpreting a statute it is charged with enforcing, and regulations adopted by the agency stand on the same footing as statutes, with reasonable presumptions to be made in favor of [763]*763their validity. See Massachusetts Fed’n of Teachers v. Board of Educ., supra; Nuclear Metals, Inc. v. Low-Level Radioactive Waste Mgt. Bd., 421 Mass. 196, 210-211 (1995); Quincy v. Massachusetts Water Resources Auth., 421 Mass. 463, 468 (1995). A court will not declare a regulation void unless its provisions cannot, in any appropriate way, be interpreted in harmony with the legislative mandate. See Massachusetts Fed’n of Teachers v. Board of Educ., supra, and cases cited.
The plaintiffs’ central contention is that the regulation’s limitation of the competency determination, or graduation requirement, to the English language arts and mathematics sections of the MCAS exam conflicts with G. L. c. 69, § ID, fourth par., (i), which states that the “ ‘competency determination’ shall be based on the academic standards and curriculum frameworks for tenth graders in the areas of mathematics, science and technology, history and social science, foreign languages, and English” and must indicate that “a particular student has demonstrated mastery of a common core of skills, competencies and knowledge in these areas...” (emphases added). Thus, the plaintiffs conclude, the regulation’s use of the MCAS exam is unlawful because the competency determination does not take into account the other core subjects mentioned in the statute.
The language of § ID, fourth par., (i), and the use of the word “shall,” has to be read to effectuate the Legislature’s purpose in passing the Act, with attention to the fact that the Legislature has entrusted the board with the Act’s implementation. The requirement that the competency determination “shall” be based on multiple subject areas cannot be construed as permissive in the sense that the board can omit entirely and permanently any core subject it chooses. We agree with the judge that, in view of the purpose of § ID to establish a certain level of knowledge and skills as a prerequisite to graduation, the statute reasonably should be interpreted to direct the board to create a competency determination including multiple subject areas while permitting the board, in its discretion, to phase in those subjects in a reasonable manner and on a reasonable timetable.
The language in § ID quoted by the plaintiffs does not ad[764]*764dress the timing or sequence of the implementation of the graduation requirement (except that it could not occur prior to 1998). There is no express prohibition in the statute concerning the phasing-in of core subjects over time and as curriculum frameworks become revised and finalized. Construing the statute to require the board to delay implementation of the competency determination until it made competence in every core subject a graduation requirement would only delay education reform and frustrate significantly the accomplishment of the Legislature’s purpose in enacting § ID, fourth par., (i), an undesirable result that is to be avoided if reasonably possible. See North Shore Realty Trust v. Commonwealth, 434 Mass. 109, 112 (2001); Watros v. Greater Lynn Mental Health & Retardation Ass’n, Inc., 421 Mass. 106, 113 (1995). “Where the focus of a statutory enactment is reform, the administrative agency charged with its implementation should construe it broadly so as to further the goals of such reform.” Massachusetts Fed’n of Teachers v. Board of Educ., supra at 774. The board, therefore, could permissibly exercise its discretion by the form of pragmatic gradualism it undertook, particularly because the fundamental subjects of English language arts and mathematics can be considered the basic foundational requirements with which other core subjects can be studied and mastered. Put more colloquially, the board could properly conclude that a student should have competence in “reading, writing, and arithmetic” before being tested on competence in science, history, and other areas.
We reject the plaintiffs’ contention that our construction conflicts with the Act’s purpose of holding educators accountable. Rather, the implementation of the regulation is a large stride in accomplishing that goal. Educators have established the required academic standards and curriculum frameworks, and have implemented the competency determination in the subjects of English language arts and mathematics. To be sure, the defendants have not been, and are in no way, excused from requiring a demonstration of competence in the other core subjects as a graduation requirement, and the defendants [765]*765acknowledge as much.13 There is no record support for, and no substance to, the plaintiffs’ argument that because the graduation requirement has not yet been based on the other core subjects, the students educated in this State with public funds are not being provided with a “comprehensive education.” Nothing in the McDuffy decision requires a graduation requirement, let alone a graduation requirement based on an assessment of multiple subjects. Simply put, enjoining the regulation, and enjoining the defendants from requiring the plaintiffs to pass the tenth grade English language arts and mathematics sections of the MCAS exam as a prerequisite to receiving a high school diploma, would undermine educator accountability and hinder education reform.
Our interpretation of the regulation finds additional strong support in two other sources. The first source arises out of other provisions of the Act that give broad discretion to the board to carry out its responsibilities. See St. 1993, c. 71, § 29.14 The [766]*766second source, which is much more direct and compelling in its emphasis, is the Legislature’s approval of the board’s use of the MCAS exam, as presently structured, to implement the Act. The approvals primarily are manifested in budget line items passed by the Legislature over the years, most particularly in FY 2003 and FY 2004, appropriating substantial sums for intensive remediation programs for those who need them in order to pass the MCAS exam.15 As the judge correctly noted, it makes no sense for the Legislature to provide for targeted remedial programs, if the Legislature did not both recognize and confirm the board’s determination that passage of the English language arts and mathematics sections of the MCAS exam was to serve as the competency determination that under the Act is a prerequisite for graduation from high school. In this manner the Legislature has expressed its acceptance of the board’s phasing-in approach. See Director of the Civil Defense Agency & Office of Emergency [767]*767Preparedness v. Civil Serv. Comm’n, 373 Mass. 401, 409 (1977); Canton v. Bruno, 361 Mass. 598, 607-608 (1972); Director of the Civil Defense Agency & Office of Emergency Preparedness v. Leger, 9 Mass. App. Ct. 737, 740 (1980). See also Boston Water & Sewer Comm’n v. Metropolitan Dist. Comm’n, 408 Mass. 572, 578 (1990); Assessors of Melrose v. Driscoll, 370 Mass. 443, 447 (1976).
3. What has been said above turns aside the additional arguments made by the plaintiffs and others16 in seeking a preliminary injunction, including the contention that the Act requires that the competency of a student be measured by a variety of assessment instruments such as those mentioned in G. L. c. 69, § II, second par., including review of an individual student’s portfolio work. Because the judge correctly determined that the plaintiffs have not shown that there is a likelihood of success on the facial challenge made, there is no need to consider the judge’s determination that the plaintiffs have not shown irreparable harm in the degree needed to obtain a preliminary injunction.
4. The order denying the application for a preliminary injunction is affirmed.
So ordered.
6The Legislature subsequently amended G. L. c. 69, § 1, specifically to include, in those children covered, a school age child with a disability as [755]*755defined in G. L. c. 71B, § 1, and a limited English proficient student as defined in G. L. c. 71A, § 1. See St. 2000, c. 159, § 134; St. 2002, c. 218, § 1A.