Not the person you replied to but for interest, It was 25 hard capped in grade school only because of the program I went through back years ago, though looking now 25-30 is petty consistent in that region as of last year. Highschool was larger, maybe 30, less once going into upper year courses, literally 8 of us took comp sci and that was combined gr11 and 12

Ontario, Canada for reference. 20 seemed low to me too tbh, but not out of the realm of possibility.