I would think most gyms that are owed tuition money would fall under Small Claims. I can't imagine a gym continuing to train an athlete that is more than several months in arrears. But they can file in Small Claims for breach of contract. Small Claims has a maximum claim amount of $5,000. It is pretty inexpensive and you don't need a lawyer. The filing fee in Iowa is $85. Then you have to have the notice served, which cost money. If Defendant does not answer or appear in court, you automatically get a judgment (probably stayed for 30 days). Enforcing the judgement could be tricky. You can garnish wages, levy bank accounts, attach real estate, etc. It will cost money to enforce and research assets and there are no guarantees of recovery. So, I don't see gym owners even taking the time to file a small claims lawsuit.
There does not seem to be a good recourse for gym owners to get tuition owed.