Dear Customer (name blocked for privacy),
Ohio has state requirements that must be met for each grade and, in addition, individual school systems may have their own requirements for a grade in addition to the state minimums. Because whether or not a student is permitted back into a school system, and what a school system will permit, is mainly a decision of that school system and its superintendent, you should contact school itself to investigate.
You should speak to his current school's administration to find out what their requirements are and what your son will need to learn, and prove he has learned, and what proof they will accept, to allow him, if and when he returns to OH, to continue with his education and not repeat a grade or material. If you can, you should try to obtain this information in writing from the school system.
PLEASE NOTE: Responses here are for information/education only, NOT legal advice and do not form attorney-client relationship! Only licensed attorneys you hire in your state can provide legal advice.