If the child was enrolled under joint "sponsorship", i.e. both parents are stated as answerable (equally ?) for the fees then the school is within its rights to turn to you for delivery of payment. However, if joint responsibility is indeed in place then both parents are in the same position and the school can be expected to (and should) make the same demand of both parents. Ultimately, in a dispute between the parents, each is liable for half the amount - providing that attitude wins and not a simple jointly-and-severally responsible, i.e either or is liable for 100% (whichever has the wherewithal and can be forced to pay). If the earlier agreement is enforcible then the one parent who undertook to pay the whole of the fees will be expected to be held liable.