We have a similar problem keepon, ds cannot generalise, so anything he learns in small groups outside of the classroom is damn near useless to him. Eg he has attended the SEAL group since he was in Reception year (he's just going into year 6), most children only go to the elements of the SEAL group that they need, so attend for maybe half a term a year or so. Ds has done the whole year, every year for seven years and can tell you the answers to any of the topics. He can tell you how you should respond in certain social situations, but, he absolutely cannot apply them if/when those situation occur in rl. So, effectively the SEAL group is a big waste of time for him and one could see it, if cynical enough, as a way of getting him out of the teacher's way for a while. (SEAL group is taught by a TA, who has no knowledge or experience of ASD and the lessons are obviously organised from an NT perspective, so fail to take into account lack of theory of mind, for example.)
He has this year been sent out of class to handwriting groups where the TA running the group sat him next to the bully who had tormented him for years and was removed from his class at the beginning of this year (bully was also right handed, whereas ds is left). She then proceeded to teach him cursive, joined up writing, despite the OT report saying he will never be able to write any better than he can now, that he should be allowed to print his letters and use technology for anything greater than a paragraph. Of course TA had no idea he had even been assessed by OT, let alone read the report and taken on board the recommendations. Again, he can practise letter formation until the cows come home, but he cannot apply it to writing he does in lessons. Yet another waste of time.
Finally, they sent him out to a maths group designed to help him (and others) learn how to handle word-based maths problems. They actually said that he was of too high a level to be in the group and that the mathematical stuff it covered was much too low for his ability, but for some reason they thought he would suddenly be able to 'get' word based problems in class because they had worked on some in this group. Again, what he did in the group, failed to inform his classwork.
So, added to his weekly session with outreach he was attending four separate outside sessions a week. Even ds knew this was a bad idea and by Easter refused to attend the groups "because I am missing important classwork and missing lessons I enjoy". If ds, a then, 9 year old boy who has AS knew it was a ridiculous strategy, why couldn't the teaching staff? Basically, because it got him out of their hair for a few hours a week.
They negotiated with him to 'drop' one of the groups for 6 weeks and he chose to drop SEAL group.
The school insist that he only requires ad-hoc 1:1 in lessons, fair enough - but if that is the case, why does he need to be removed from the class several hours a week?
Anyway, that's by the by. Is the assessment you mentioned Statutory Assessment for a Statement? Are you in the process of trying to get him a statement yourself?