On Monday, 7 December 2020 at 15:30:12 UTC, Phoenix wrote:

Thank you for your reply. I have a 14 year old glider student who has Asperger's. You wouldn't notice he had "issues" except that he has difficulty keeping eye contact with those with whom he was talking. Concerns I had / have a
1) Comprehension of glider training texts
1) Physical ability to manipulate three axis control
3) Ability to put aviation knowledge into actual practice
4) Ability to multi task - especially under pressure

As it turns out, he is flying gliders exceptionally well, performing above the norm. His comprehension of the training tests is now of no concern. His actual flying is butter smooth. My concern is...... should I solo him (when ready) or require him to only fly with a qualified ride pilot?

I'm not an expert on psychological/psychiatric matters, much less a clinician (see v. recent reply to Jim Kellet).
But I would say that the solo question needs to be handled the same way as with any other student. How do we do that? Who can say, apart from from observation, and judgement of character based on our own experience as instructors. And of course we will have put them through their paces more than once without *any* help or encouragement of any sort: if asked about anything on such a flight I have a stock reply "You're flying it!", always delivered in the same flat voice, even if I am within a couple of seconds from taking over! It's amazing how much a pupil can read your mind ... but some (at any age) can be unduly unsettled by an anti-social stony silence.
I would say that consistency from day to day, and resilience to pressure and emotional distractions are of more concern with the very young - whether Aspies or not. I have flown with several students that young: mainly they were fairly mature in their approach, but none of them happened to be close to solo. Of course, many adult students also have difficulties with your listed concerns!
J.