Look at his most recent IEP to see what his written goals are and what percentage of these need to be met for the intervention to be deemed successful. Keep in mind that an IEP is a legal contract, to which the school district is a party. If these goals haven’t been met they’re still bound by the terms of the IEP. If it’s time for the IEP to be renewed, you don’t have to agree to new terms, the Section 504. Check on this, but I think the current support services stay in place until new terms are agreed on. Also check to see if there are any Special Ed/legal agencies in your area that can advise you. You have more authority than you think you do, though this whole process can be very intimidating. Good luck!