What is the ruling on not completing the payment of a school installment after the child has completed the entire academic year?

It is not permissible for one who is able to procrastinate in paying the installments due to the school, as this is a forbidden injustice. As for the one who is in hardship, he must be given respite until he is able to pay. If the school agrees to waive the installments, there is no objection to that.