Dooley, J.
This is an appeal taken by plaintiff-mother Gail deBeaumont from a modification order of the Orange Family Court that shifted parental rights and responsibilities of the parties’ children from Ms. deBeaumont to the defendant-father, Mark Goodrich. We affirm.
The parties were married for eight years before separating in 1990 and divorcing in August 1991. They had two children during their years together: Stephen, born in December 1985, and Molly, born in May 1988. Prior to separation, the mother provided care during the day for the children while the father worked, and both parents shared caregiving responsibilities during evening and weekend hours. After the separation, the mother returned to culinary school and worked periodically, with the parties splitting care. The children also continued to visit their paternal grandparents two to three times a week as they had been doing since birth.
Upon divorce, the mother was granted sole legal and physical responsibility for the children. The father was granted parent-child contact that allowed him to have the children for three days each week. This arrangement permitted continuation of the parties’ practice of co-parenting. As part of the final decree, the court included a paragraph drafted by the parties stating: “If either party moves more than fifty (50) miles from their current homes in Thetford and Norwich, it shall constitute a change in circumstances so the Court may reconsider existing parental responsibilities and visitation.”
On January 25, 1992, the mother chose to leave her home in Thetford and move to Milford, Pennsylvania, to join her companion, John Diefenbach. She consulted her attorney before doing so and was told that a move with the children would lead only to a reopening of parental-child contact issues, not a redetermination of all parental rights and responsibilities matters. Thereafter, the mother picked the children up from the father’s home, and informed him for the first time that she and the children were leaving the state. She had not told the children they were moving to Pennsylvania, nor did she tell her [95]*95son’s school that she was taking him out of state. The mother refused to give the father the children’s mail address or telephone number for a week after the move and continued to refuse to give him her street address.
In response to a February 5 order of the family court, the children were returned to Vermont in early March. On March 25, the family court awarded the father temporary parental rights and responsibilities and gave the mother parent-child contact every weekend and Easter vacation. For purposes of assessing parental care, the court required a family evaluation. This evaluation was performed in May by Dr. Donald Hillman, who found that the children did not perceive either parent as the primary caretaker; rather, they considered both equally caring and committed. On August 24, 1992, the family court modified its earlier order and granted sole legal and physical responsibility to the father, subject to parent-child contact with the mother.
On appeal, the mother argues that the family court’s decision to modify should be reversed because the court’s findings were insufficient to warrant the modification, that the modification violated the teachings of Lane v. Schenck, 158 Vt. 489, 614 A.2d 786 (1992), and that it was error for the court to adopt many of the findings of the family evaluator but reach a conclusion contrary to the evaluator’s recommendation.
In order to modify a custody determination, a moving party must traverse two hurdles. First, the moving party must make “a showing of real, substantial and unanticipated change of circumstances.” 15 V.S.A. § 668. Once that threshold is met, the moving party must then show that annulling, varying or modifying a prior parental rights and responsibilities determination is in the best interests of the child.1 Id.; see Kilduff v. Willey, 150 Vt. 552, 553, 554 A.2d 677, 678 (1988) (only if court finds substantial change of circumstances may it consider best interests of child).
In this case, the father argued that his burden to overcome the first hurdle was met by a provision of the divorce order, based on a stipulation of the parties, concerning the impact of either parent moving more than fifty miles from their respective homes in Vermont. The provision stated specifically that such a move “shall constitute a [96]*96change in circumstances so the [family] Court may reconsider existing parental responsibilities and visitation.” We agree that the provision provided the family court with a reasonable basis to find changed circumstances.
There is no specific statutory authority for the divorce order to define changed circumstances for purposes of a future modification, nor have we considered such a provision. Without deciding whether such provisions will always be effective, we conclude that this provision was effective in this case for two main reasons.2 First, it was based on a stipulation of the parties. The Legislature has provided that an agreement between parents concerning the division or sharing of parental rights and responsibilities is presumed to be in the best interests of the children. See 15 V.S.A. § 666. The changed circumstances provision was part of such an agreement and is entitled to that presumption. There is no reason to overcome such a presumption in this case.
Second, the provision established a reasonable benchmark to determine changed circumstances. Although physical responsibility for the children was awarded in the divorce decree to the mother, the time allocation for each parent was nearly equal so that a co-parenting arrangement was present.3 Through the stipulation, the parties specified the limit to which their residences could be separated and still make the co-parenting relationship work. They agreed that if the distance limits were exceeded, the arrangement would break down so it would be necessary to reconsider the custody and visitation provisions in the divorce order. The specific distance standard enabled the parents to plan their lives with a clear understanding of the expectation of the other and the possible consequences of a decision to relocate.
In reaching the conclusion that the provision provided a basis to determine changed circumstances, we want to distinguish the [97]*97provision from one that would automatically change custody because of a relocation by the physical custodian. We would not give effect to an “automatic change” provision “because it is premised on a mere speculation of what the best interests of the children may be at a future date.” Hovater v. Hovater, 577 So. 2d 461, 463 (Ala. Ct. Civ. App. 1990); see also Wilson v. Wilson, 408 S.E.2d 576, 579 (Va. Ct. App. 1991) (“predetermined” change of custody based on future move is an abuse of discretion). Here, the provision dealt only with the threshold; any changed custody had to be based on an independent assessment of the best interests of the children.
The mother argues that even if the provision is valid, it does not authorize a change of physical responsibility, as opposed to a change in visitation. The language of the provision covers both “visitation” and “parental responsibilities.” Compare Dunning v. Meaney, 161 Vt. 287, 291, 640 A.2d 3, 5-6 (1993) (agreement that change in circumstances could necessitate change to “the visitation schedule” was not applicable to modification of parental rights and responsibilities). The changed circumstances determination applied to custody as well as visitation.
Even if there had not been a provision in the divorce order, we would uphold the family court’s conclusion that the mother’s move of the children from Thetford to Milford, Pennsylvania, was a real, substantial and unanticipated change of circumstances. There are no fixed standards for determining what meets this threshold. Kilduff, 150 Vt. at 553, 554 A.2d at 678. We have emphasized, however, that in order to ensure stability in the lives of the children, the burden of showing changed circumstances is “heavy.” Id. Although relocation “often triggers jurisdiction under the modification statute,” Lane, 158 Vt. at 496, 614 A.2d at 790, the physical custodian has a right to determine the child’s residence, and relocation without more is not per se a substantial change of circumstances. See Lenders v. Durham, 564 So. 2d 1186, 1188 (Fla. Dist. Ct. App. 1990); Smith v. Mobley, 561 N.E.2d 504, 506 (Ind. Ct. App. 1990); VanName v. VanName, 419 S.E.2d 373, 374-75 (S.C. Ct. App. 1992). Any relocation will, as a matter of course, involve disruption and change in children’s lives, but a court must not confuse its analysis of changed circumstances with its determination of the children’s best interests. Rather, “‘[w]hether or not any given change is substantial must be determined in the context of the surrounding circumstances.’” Smith, 561 N.E.2d at 507 (quoting Poret v. Martin, 434 N.E.2d 885, 890 (Ind. [98]*981982)). Further, “it is the effect upon the child which renders a change substantial.” Ohman v. Ohman, 557 N.E.2d 694, 696 (Ind. Ct. App. 1990).
We also emphasize that the “threshold decision for a motion to modify is discretionary,” Lane, 158 Vt. at 494, 614 A.2d at 788, just as the initial parental rights determination is within the court’s discretion, see Myott v. Myott, 149 Vt. 573, 578, 547 A.2d 1336, 1339 (1988). As a result, whether an initial determination or a modification, this Court “must affirm unless the discretion [was] ‘erroneously exercised, or was exercised upon unfounded considerations or to an extent clearly unreasonable in light of the evidence.’” Id. (quoting Jensen v. Jensen, 141 Vt. 580, 581-82, 450 A.2d 1155, 1156 (1982)).
We upheld a trial court’s determination of changed circumstances in Lane when the mother proposed to move to Iowa with the three minor children to attend graduate school. 158 Vt. at 494, 614 A.2d at 788. In that case, the father was entitled to visitation during alternate weekends and holidays. The change in circumstances is even more substantial here. Although the distance was greater in Lane, the distance is great enough in this case to prevent extensive visitation. Here, the mother unilaterally terminated the parties’ co-parenting arrangement by removing the children to Pennsylvania. In so doing, she deprived the children of day-to-day contact with their father and with their paternal grandparents, subverting, as the trial court found, “[t]he financial, education, housing, and co-parenting plans agreed upon by the parties [which] had as a central element that [the mother] would be residing in the marital home in Thetford and that [the father] would be living in close proximity to her.” Additionally, the son changed schools, leaving a school in which he was a recognized leader, and both children left a supportive community, which included their father’s church community. The move triggered a breakdown in communication, and the father was unable to contact the children at all in the first few weeks. See Day v. LeBlanc, 610 So. 2d 42, 45 (Fla. Dist. Ct. App. 1992) (A move may constitute a substantial change of circumstances if the distance is far and the visitation of the other parent will be subject to significant interference as a result.). There was no abuse of discretion in finding changed circumstances.
Having met the initial hurdle of showing real, substantial and unanticipated changed circumstances, a parent moving for modification of custody still faces the burden of showing that a change in parental responsibilities is in the children’s best interest. 15 V.S.A. [99]*99§ 668. As we discussed at length in Lane, a finding of changed circumstances does not alone mean that custody should be modified. See 158 Vt. at 496, 614 A.2d at 790. The residency decision of the custodial parent is entitled to deference and “giving stability to a child’s life, to the extent possible under the circumstances, is so important that custody ought not to be modified without critical justification.” Kilduff, 150 Vt. at 553, 554 A.2d at 678-79.
The trial court made extensive findings in support of its decision that it was in the best interest of the children to shift legal and physical responsibility to the father. We can summarize only the highlights of these findings. The most important finding was that prior to the mother’s move neither parent was more “primary” than the other and that both were fit parents. The court found both parents to be dedicated, caring, sensitive, conscientious, moral and effective; and both have strong and natural bonds with the children. The children desired to stay together.
In favor of the father, the court found that he was content in a good job and has a steady disposition with the children. Custody with the father allowed the children to remain in a community, and in the case of the son a school, in which they had done well. It also allowed continuing contact with the parental grandparents, who had become very important in the lives of the children. The father was more likely to foster a good relationship between the children and the mother than vice versa.
The court emphasized the strong parenting skills of the mother and found that she has greater insight into her emotional problems than the father so that she “can provide emotional richness and variety to her children’s lives in a way that [the father] cannot.” It found, however, that the move to Pennsylvania was made solely for the convenience of her companion and was not done in a way to allow an orderly transition for the children. Overall, it found that the mother “has had difficulty gaining her own direction since the separation, which has led to a fairly high degree of instability in her life.” It was concerned that the mother had allowed the companion to use corporal punishment on the children, although the mother was opposed to such punishment. The move weakened the mother’s financial circumstances because she gave up a mortgage subsidy on her home in Thetford in order to move into an apartment costing $500 more per month although she earned only $5.25 per hour. The court found she was less willing than the father to foster cooperation and a positive relationship with the other parent.
[100]*100Each parent exhibited some behavior which the court labeled as a risk factor. In each case, the court found that the behavior was not displayed before the children and thus did not affect the custody determination.
The mother faults the custody determination in three respects: (1) it is inconsistent with the decision in Nickerson v. Nickerson, 158 Vt. 85, 605 A.2d 1331 (1992), because it gives inadequate weight to her role as primary caregiver; (2) it is inconsistent with the standard for changing custody announced in Lane; and (3) it improperly deviates from the recommendation of the family evaluator. We take these claims in order.
The mother first argues that Nickerson and Harris v. Harris, 149 Vt. 410, 546 A.2d 208 (1988), direct the family court to determine who was the primary caregiver in the preseparation period, and to award custody to that person unless he or she is unfit. She argues that she was the primary caregiver both before and after the parties’ separation.
The language on which the mother relies is in Harris:
We do agree, however, that this factor should be entitled to great weight unless the primary custodian is unfit. The exact weight cannot be determined unless there is evidence of the likely effect of the change of custodian on the child. In the absence of such evidence, the court should ordinarily find that the child should remain with the primary custodian if that parent is fit.
Id. at 418-19, 546 A.2d at 214 (footnote omitted). She interprets Nickerson to hold that the period for determining the primary custodian is prior to the separation.
For three reasons, this argument is unavailing. First, the Harris and Nickerson decisions involve determining the physical custodian in the initial divorce decree. The question of who is the primary caregiver prior to separation, even assuming it can ever have the overwhelming weight the mother desires, cannot determine who should have physical responsibility in a modification decision. The whole point of the modification process is that changed circumstances may have made the initial decision inappropriate, so a reexamination of the interests of the children is warranted. See 15 V.S.A. § 668. To give special weight to the preseparation, predivorce caregiver would make modification unlikely even if circumstances had changed and the interests of the child clearly warranted modification. In short, it would introduce a factor irrelevant to those in the statute.
[101]*101Moreover, the argument misreads Nickerson. In Nickerson, we specifically avoided a per se rule, “declin[ing] to follow the unyielding approach of some courts which bifurcate the pre- and post-separation periods in determining the primary-care-provider.” 158 Vt. at 90, 605 A.2d at 1334. Rather, we held that a court’s “inquiry should focus on all relevant periods of the child’s life.” Id. at 91, 605 A.2d at 1334. For purposes of a modification motion, of course, the most relevant period is that between the divorce and the filing of the motion to modify.
Second, the trial court specifically found that neither parent was the primary caregiver in the post-divorce period. The specific finding of the court was “neither [parent] is more ‘primary’ than the other, either by virtue of the quality of the care each provides or the amount of time each has spent providing it.” Although the mother disagrees with this finding, it is supported by the evidence and is not clearly erroneous. The finding defeats her argument that the decision is inconsistent with Harris and Nickerson.
Third, Harris specifically decided that the weight to be given to primary caregiving is to be determined in light of the “effect of the change of custodian on the child.” Harris, 149 Vt. at 419, 546 A.2d at 214. Only when there is no evidence of that effect should the court ordinarily find that the child must remain with the primary caregiver if fit. Here, there was extensive evidence of the effect of change in the lives of the children, including the effect of a change of primary custodian to the father. The court’s decision analyzed the impact of change at length. The Harris analysis of the decision-making process in the absence of such evidence and consideration does not apply here.
The mother’s next argument is that the trial court’s decision is inconsistent with Lane. She stresses the standard Lane announced to modify custody because of a relocation: “To prevail, the noncustodial parent must prove that the children’s best interests would be so undermined by a relocation with the custodial parent that a transfer of custody is necessary.” Lane, 158 Vt. at 499, 614 A.2d at 792. She argues that the findings the court made in support of the modification would be true in any relocation case: the children would be removed from their former friends and classmates, it would be more difficult for the noncustodial parent to visit with the children, and there would be less contact with the parental grandparents. She emphasizes that Lane holds that she is entitled to determine the place of residence of the children, and the court may not second guess that determination. Id. at 495-96, 614 A.2d at 789-90. Therefore, she argues, custody cannot be modified because she exercised her right to determine the [102]*102residence of the children, and the normal consequences of that decision ensued.
This case arises in a context different from that in Lane, and that difference is critical to the application of Lane. In Lane, the court did not modify physical responsibility. It modified the divorce order to impose a condition that the mother not reside more than a four-hour drive from the father’s residence. In essence, this order was no more than a “you may not move” order, and we rejected the court’s failure “to show sufficient deference to the mother’s decision to relocate.” Id. at 491, 614 A.2d at 787. Specifically, we refused to “condone a process that substitute^] the judgment of a court for that of the custodial parent merely because the court would have done something different if it had been the parent.” Id. at 495, 614 A.2d at 789.
The mother is arguing here that Lane, although not directly about modification of custody, imposes a special standard for such modification in relocation cases. We disagree.4 The modification statute imposes only one standard: whether modification “is in the best interests of the child.” 15 V.S.A. § 668. As discussed above, because of the value of stability in a child’s life, we impose a heavy burden on a noncustodial parent to show that the best interests of the child have so changed that the extraordinary step of custodial change is warranted. That burden is neither greater nor different in custodial-parent relocation cases.
Contrary to the mother’s argument, four factors differentiate this case from the ordinary consequences of relocation and underlie the court’s modification order. The most important is the co-parenting relationship, which meant both that the loss to the children from the relocation was very great and that the father was prepared to assume the responsibilities of custody with little modification of his life.
Second, the father’s parents played an unusually strong role in the lives of the children. The family evaluator found:
[The grandparents] appear to have been a strong source of nurturance and support over the years. They appear firmly and [103]*103positively bonded with the children, connections equally experienced by the children. They (and their rural setting) seem to have been a source of stability for the children.
The court adopted this finding. The relocation necessarily reduced the value of this resource to the children. The change of custody restored it in part.
Third, the manner in which the mother relocated was not in the best interest of the children since she did not prepare them for the move, and it unnecessarily interrupted their relationship with the father.
Fourth, the mother’s actions since the divorce, and the reasons and consequences of the relocation, pointed to continuing instability in the lives of the children, as well as financial hardship. The father’s life promised greater stability. See Kilduff, 150 Vt. at 554, 554 A.2d at 679 (“It is hard enough to give children of a broken home some semblance of an ordered life, while at the same time maintaining adequate contact with both parents, without subjecting them to the further disruption of moving to a new home . . . .”); Wells v. Wells, 150 Vt. 1, 5 n.*, 549 A.2d 1039, 1042 n.* (1988) (importance of stability in lives of children of divorced parents widely recognized).
The trial court has broad discretion in a custody matter; we cannot set aside its decision “because we would have reached a different conclusion from the facts.” Myott, 149 Vt. at 578, 547 A.2d at 1339. The court made an extensive review of the custody factors set out in § 665(b) in evaluating the best interests of the children. It acknowledged the heavy burden on the noncustodial parent and required him to meet it. It emphasized the considerations other courts have used to order a change of custody in relocation cases. See, e.g., Smith, 561 N.E.2d at 507 (change of custody promoted stability in schooling, community, social, church and family relationships); Schubring v. Schubring, 476 N.W.2d 434, 436 (Mich. Ct. App. 1991) (stability and success in school); KR(S)D v. CDS, 646 S.W.2d 428, 431 (Mo. Ct. App. 1983) (family ties and support for visitation by noncustodial parent); McMahon v. McMahon, 607 A.2d 696, 702 (N.J. Super. Ct. 1991) (co-parenting); Nichols v. Nichols, 792 S.W.2d 713, 716 (Tenn. 1990) (close relationship between noncustodial parent and children). We do not agree with the dissent that the petition to modify should have been dismissed as a matter of law because no view of the evidence could support modification. We find no abuse of discretion. See Dunning, 161 Vt. at 289-90, 640 A.2d at 5 (as long as findings [104]*104reasonably support judgment, family court’s decision must be upheld).
Finally, the mother argues that the court was in error for adopting findings of the family evaluator, Dr. Hillman, but making a modification ruling contrary to his recommendations. In fact, Dr. Hillman’s main recommendation was that the parties attempt to reach a joint custody arrangement for the sake of the children. After discussing the benefits of a mediated custody agreement, Dr. Hillman stated that “[w]ith John [Diefenbachj’s support and involvement, together with individual counseling, [the mother] would seem to be in a slightly better position to be the parent with primary physical custody, if that has to be the case.” After citing positive reasons for placing the children with the mother, such as her greater comfort with and knowledge of younger children than the father displayed, Dr. Hillman cited certain negative aspects of the mother’s personality, such as the mother’s dependency needs and insecurity that she was likely to project on to the children and the father. Dr. Hillman did note that the negative factors were actually a reason to keep the children with the mother, on the theory that losing physical responsibility would exaggerate the negative factors, and particularly the mother’s inclination to charge the father with sexual abuse, charges which she had made in the past and had proved to be unfounded.
The court may disregard the recommendations of the expert. See Bissonette v. Gambrel, 152 Vt. 67, 71, 564 A.2d 600, 602 (1989). The findings make clear that the court did not see the mother’s companion as a resource to make her the better custodian. Indeed, the court specifically rejected consideration of the companion as a resource because he had “no legal obligation, family tie or emotional bond to the children.” It also rejected that it should determine custody based on the mother’s reaction to a loss of custody. In fact, the court found that the mother’s stress over the divorce and separation from her children was a negative factor to be weighed against the father’s ability to provide a stable home life and continuity in relations with the other parent. The court adopted many of the findings of the family evaluator, and considered his recommendation, but the ultimate responsibility to decide lies on the court, not the expert witness. There is no error in the use of the expert opinion.
Affirmed.