Note: The DearEsq free 'ask a lawyer' site is offered as a free informational service to the public and is not intended as legal advice. Laws vary from state-to-state, and in addition every situation is unique, and relevant facts may not be known. The answer to the question posed below may not apply to in your state or to your situation. For legal advice in your state and your situation you should consult with an attorney in your state who is familiar with the rules and laws in your state.
‘If my son’s mother and I agree on a visitation schedule, write it out and sign it will it be legal if she decides to go to court in the future?’
Question: It seems that what you are asking is whether the Court would enforce the agreement. In family law, a Court is usually unable to actually enforce a privately written agreement that has not been entered as an order by the Court. However, the longer that everyone has been abiding by the agreement, the more likely it is that the Court will at least consider that the arrangements should be honored.