Sorry only just seen this.
I didn't really have problems as such in school, nothing strong enough to get assessed anyway, but if I look back the signs were there.
I struggled socially. Didn't ever really fit in with a peer group. School work itself was okay when the format was a class/small group discussion or worksheet with questions and answers but anything where I had to write something longer you can tell that I couldn't stay focused on it and it would either trail off really early or the writing would start to move off the lines - this got better in senior school where I was more able to write longer pieces, but anything where we were given freedom, I just wouldn't do enough of it. That didn't really become apparent until GCSEs and coursework and by then I was established as a good student so I was given the benefit of the doubt rather than pressure over it. I really needed the pressure/support, though.
Terrible handwriting. General scruffiness to my work even though I tried to keep it neat. Homework always done at the last possible minute unless threatened with dire consequences otherwise.
I didn't get out of my seat or disrupt the class. Apparently, that's rarer in girls. I did used to fidget constantly. I'd take my shoes off in the middle of the lesson to slip them back on (nobody noticed), roll my socks back and forth, sit with me feet up on the chair, in primary school I used to suck my clothing (I don't remember this, well, OK, I remember one cardigan tasting nice 
) and apparently my year three teacher told my mother that I was "disturbed" 
because I used to rub the label in my knickers for comfort and she thought I was "touching myself" in the class. 
Long term I think what it looked like, and what I assumed myself for a number of years, is that I was intelligent enough to coast for most of the time on very little effort and then when the work started to become challenging I struggled because I didn't really have the skills to study, because I'd never needed them before. I now know that this is false, and what happened was everything was okay for me when my time was being managed for me, I was told go here at this time, go there afterwards, do this small chunk of work, now do this, and other people were able to take this structure and apply it to their own work but I am lost without external structure. So coursework and post-16 was a nightmare for me. I actually looked through my year 10/11 school records as part of my assessment recently, and I missed almost all of my projected grades, the final grades I received in almost all subjects were the exact same as the grades I was working at in year 10, effectively I made zero progress in that year despite always having been a good student. I then went on to struggle and gain low marks in two post-16 placements (BTEC and A Levels), became jaded/depressed, got into drinking, smoking, drugs, got pregnant at 19 (hopefully not a problem for your DS!) - I did end up going back to uni at 21 but I found that difficult as well, everything was OK when I was stuck in a very limited schedule because of my DS but as soon as those rails were taken away I lost everything again. Messed up some exams, forgot to go to the resits, threw away a whole year's work. I think I might be ready to try it again this year but I'm nervous.
Diagnosis is relatively recent but has enabled me to access support knowing for sure that this is what the problem is for me rather than speculating. I also have the option to try medication but it's not something I've tried yet.