Start by making official objections in writing. Make it clear you are building a case against her. Then build the case and maybe she'll fold.
If he does, great. If she doesn't you should have a solid case of notifying her of her objection and offering reasonable alternatives that provide continuity for the kid and the least amount of aggravation for the both of you. Not that the law necessarily supports you being able to even bring a case.
Then take it to a judge and hope for the best if you can even get it heard,
What does your decree say on the subject?
For instance, mine says we share joint legal and I have final decision making authority regarding the kids education. That means I can put them in whichever school I want. Your parenting plan should say something about it or should outline how disputes are handled.
Georgia Code 19-9-1 Section 2 paragraph E says ,
Unless otherwise ordered by the judge, or agreed upon by the parties, a parenting plan
shall include, but not be limited to:
An allocation of decision-making authority to one or both of the parents with regard
to the child's education, health, extracurricular activities, and religious upbringing, and if the
parents agree the matters should be jointly decided, how to resolve a situation in which the
parents disagree on resolution; and
Also, if your decree doesn't contain the statutory requirements of allocating the decision making authority you should expect it to after you take a case to court for enforcement.