I would ignore his unreasonable demand that you cease communicating with the teacher. I can't imagine what he can claim that you have done to warrant that kind of treatment. If you want to be nice, then cc him on your commuications. Of course, he always has the right to respond on behalf of the teacher.
The settlement agreement is probably boiler-plate. I would decline to sign if and only if you are actually giving up rights that you believe you will be invoking. Furthermore, some rights you cannot sign away in certain circumstances. Harm from future incidents in school should fall under that category. The statute of limitation for minors doesn't start running until their 18th birthday.
There is also the issue of whether the District is required to provide the vision therapy. I seem to recall that certain medical treatments, even if your DS needs it, the District is not obligated to provide.
