For evals, I like getting a private one done 1st, not by the therapist the school uses. You can read the report, find out what's going on and decide whether or not you want that included in your child's educational record.
If you are trying to get services and the private eval says that there are things going on then it's up to the school and their therapists to say oh no, that Dr or therapist your child went to is wrong... not that they will automatically say sure thing we'll provide therapy... but they will less likely to deny services.
If you find out something you just don't think is any business of the schools, there is nothing out there that says you have to give them your childs in depth medical records, hey can ask, you can say no.
Don't ever fill out a medical release of information for the school to request paperwork, if they want a report, tell them you will get them a copy or write a very specific release... such and such test that was preformed on X date and only allowed to request 1 time and that the request expires on a certain date.
I haven't actually done this but I am planning on giving the school some medical reports that have whole lines and areas blacked out, it's none of their business and it does not affect his education/ability to learn or to function that he has ____ or ____. There are some things too in his medical reports that don't affect his education directly but I will leave them in because those diagnosis are useful in understanding who is is, the other things are just too personal and I don't trust that the school will keep them private.
FWIW, our son did have an OT eval (privately) and I wasn't really asked to fill out a questioneer like the one linked, he has physical hand deformaties and a concreate 'why' behind the reasons he does or doesn't do things like everyone else..... Although it looks very similar to where we were intially susposed to go.... the scheduling lady at our primary docs office had made the referal to a 'developmental' specialist of some sort, when I got his paperwork in the mail to fill out the questions started with behavior and disipline and social stuff... I called that Dr's office because I didn't like the possible path that might lead down (honestly if there is a 'problem' like that going on with him I'm not ready mentally to deal with it right now..... plus I doubt there is.... or is that just denial

) either way I just wanted someone to test his actual abilty to do things physically and show us ways to help him improve the skills he has and work with the function he has.... The developmental place told me I could skip their step (because of the obvious physical deformaties) but that was their office was usually the 1st step in trying to figure things out... not saying that your school may go about it the same way with the developmental eval that leads to the OT... but be prepared just in case and do a little reasearch on what type of testing they want to do before you consent....
All that said I really think evals that aren't invasive physically don't 'hurt' - are positive and a good thing. Having more informaion about something is usually a good thing. It's who has that information and what they do with it that isn't always positive. Get your own elval done.