I would refer to your insurance policy on this, is it because of his condition, or does your insurance only cover 90 visits combined a year? There is a big difference on that.
I am an appeals nurse for an insurance company so I can help on this but we need to know plan language first and foremost. If they are denying based on diagnosis then you can appeal for treatment as long as he is showing improvement towards measurable goals and functional deficits. At his age I am sure his short term and long term goals are ever changing and he should still be showing improvement towards his goals. My Son is almost 8 and is still showing improvements and gains towards his goals on his treatment plans.
Get a copy of the exact plan language and your EOB denial if you'd like some help and let me know what it says and we can work from there on what kind of appeal chances you have an what you need to do to appeal.
It is so much harder to obtain coverage once they are not walking, or there is no acute need for therapy. Medicare even requires acute need, they do not pay for maintenance care. For many insurance groups you can get your 90 visits and that is it and your appeal will fall on deaf ears. Once they are not showing improvements you still would want to be able to show the medical necessity for whatever therapy you are providing. As a nurse you know there is still a need to prevent contractures, foot drop, blood clots,etc...even pool therapy can provide some improvements for boys that are immobile if they are given the chance. The key is to make sure the medical necessity is shown, have a strong treatment plan in place and then show that the treatment plan is being executed.