Hi Chinasmum.
Does your son have The Art of Wrist Spin bowling by Philpott? I suspect the answer is yes, but if not it buy it for him and it will help him persevere and get through the tough times. It's the next best thing to having a coach.
That's great thank you for that tip, have just purchased for him!
It's interesting that some of you say that bowlers that have more vertical arms are better with wrong 'uns / top spinners but generally not side spin. I have a near-vertical arm height and consider myself much more of a side spin bowler than a top spin bowler. My stock ball is the 45 degrees leg break which is in between but I use the square spinning leg break frequently and my wrong 'un definitely isn't the best there is. But I suppose it has something to do with my flexible wrist, it's so flexible that I can almost bowl the wrist doosra
not over a full 22 yards though... Guess I'm just an exception to the rule. ( if there is a rule that high arm bowlers are better at top spinning deliveries )