@lostaccount I agree with you he might not be able to get a lawyer, and I said as much. Now on to the rest of your comments.
If would be very, very easy to show that he would have made NMS had he had the extra five minutes. The SAT has already dealt with this issue, and they have just excluded a portion of the test from the scoring. You could simply look at the performance on the first two-thirds of the section, for example, and extrapolate a score from that. Damages would vary, depending on where plaintiff wanted to go to school, from a few thousand dollars to $150,000 or more. And it is possible to calculate the harm done to admission chances by not being a NMS; courts make these types of judgments daily. That’s what they are there for. As for the issue of whether it was volitional, it was. She had knowledge that she was doing it, and she did it.
Why would the teacher be immune? I have never heard of teacher immunity in my entire life. There was a duty; the proctor breached her duty; there was possible harm; there is a remedy.
I think the toughest legal hurdle for the OP is that the College Board provided a remedy for this problem, which was to notify them and have his scores cancelled, and I said this in my original post. I still the the scumbag witch deserves to be sued, and if the OP can’t find a lawyer to take the case, he ought to just go online and see how other people have drafted legal complaints and file his own. If nothing else he will draw attention to what a terrible person the woman is and make sure that she never harms any more students.