I guess the question is do you feel the school is doing everything they can to help him reach his full potential? Having learning disabilities of any kind mean he will likely always be behind his peers who do not face that same challenge and is going to need supports of some kind to reach his personal achievement goals. “grade level” is less important IMO than ensuring that a child is learning everything they can at their pace and is continuing to grow and develop their skills steadily. If your goal to get him back in the public school system is because you feel that system can better meet his needs, then I would sit down with your district’s SPED team and see where they feel he needs to be to successfully re-enter their system. If you DO feel the therapeutic school is helping him find his way forward and is maximizing his potential and you feel he is successful there then I would worry less about benchmarking him against standards and focus more on his personal progress. All that said, if you ultimately want him back in a mainstream school he will likely need to close his current gap and be closer to grade level standards before entering middle school. A strong foundation of basic skills is important at that stage because the way of learning and the expectations change significantly. If he enters the MS environment without solid reading and math skills along with some level of executive functioning skills it will be very difficult for him to progress successfully thru the public system. At the end of the day if it were me and I were happy with his current school and his personal achievements I would leave him there and focus more on maximizing his personal potential in an environment that understands him, his needs, and let him take the path forward that his personal needs call for.