The college may hold the custodial parent responsible for educational expenses, but the question of apportionment should have been in your divorce decree, seperation agreement or order dissolving the marriage and apportioning property. For some expenses State law can hold both parents liable for the entire amount. If the child is emancipated and the expenses are not gauranteed by the parents then the parents may not be liable for any of the expense if it is not stated in the divorce decree.
A judge has virtually unlimited discretion to allocate college expenses among the parents and the college student, too. The incomes of each parent and the college savings accounts if any can be used. A judge will also look to relevant New Jersey case law to decide that issue.
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Your divorce decree or property settlement agreement should specify what costs are attributable to each parent, and the percentages, If not, you may have to file a notice of motion with the court to determine who is responsible for what costs after your student applies for all loans, grants, and financial aid...