My divorce was final in Indiana. My ex pays support and also is supposed to pay for our son's college education as noted in our divorce agreement. However, he must think I forgot what it said. When presented with the remainder of the bill for our son's first semester, he wrote the school and told them since he pays me (an exaggerated amount) of child support that should cover those expenses that were not covered by scholarships, grants,. I cannot afford an attorney. Should I need one to go back to court?
He is a federal employee, living quite comfortably. I don't understand why he is trying to get out of his obligation.

Send him a copy of the court order and a bill. Give him 10 or 15 days to pay it, and tell him you will take him back to court for contempt if he does not.
If he does not pay, you will have to take him back to court.

What exactly does it say about the payment of education expenses? If he is already paying support and if it includes a continuation of child support through 21 provided there is extended education then he may not owe anything extra. Also a judge may ask that the costs be split between the parents as you are both responsible for the child. Look carefully before making any threats.