The oral pronouncement of the judge is a valid court order. Purposely failing to abide by a court order "could" result in contempt of court. Enforcing a court order that didn't make it into writing may be difficult for obvious reasons. You should seek a modification to be safe.
Do not disobey the court's order, the consequence could be severe, the better thing is to go in for a modification and explain your situation to the judge. You may also want to get a supportive letter from the school staff. If you do it on your own you risk contempt charges, including possible loss of custody and a fine?
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