Is Vision Therpay Legitimate?

We have a son who has had trouble in school. Much of the problems have been attributed to problems in vision as in the eyes not tracking together. This was given to us by a OT and of course the Vision Therapist tried to sell us on it. Are vision therapy exercises worth the effort? Is it a hoax? You can view what a session generally looks like . . .

http://www.youtube.com/watch?v=oYD9nNc2yAI