My sons have severe ASD, non verbal with ADHD.
I got an A* for English and History.
My Maths GCSE was a D (just about that!)
My Biology was an A... my chemistry and science a D bringing my overall grade down by a lot (I can't remember what it was now)
I really, really wanted to pay attention but my brain just flew away with the fairies if it wasn't stimulated into focusing. If I wasn't interested in it, as in genuinely curious and enjoying the material, my mind ran.
It would go something like this... a maths teacher would say 'right, this is why this triangle's x = 90•
My mind would think right, focus now! And then it would say '90, that's a good age to be. Must be good to get to 90. Think of all those years. That reminds me, nanny is getting old. What would she want me to remember about her? My brain would then start playing 'DO YOU REMEMBER' the earth wind and fire song 
And I would be full of self hatred that I just couldn't bloody concentrate! I tried and kept failing
In English and History I would wow the teachers with a lot of extensive knowledge and already read the material they were giving us to work on. I was genuinely interested and enjoyed it.
There was a parallel universe going on at parent's evening - one teacher describing a chatty, involved and clever student who took a lot of interest and produced great work (if sometimes late). The other saying I don't pay attention and look like I'm daydreaming a lot with very poor maths skills well below expected
My parents weren't very interested in my academic achievements at all and had a lot on because they had 3 toddlers when I hit secondary school
Would it really have been any better for me if someone was pushing me externally?
For what it's worth, I am a paramedic now. But I left school with next to nothing and didn't do any A Levels. I only made this choice in my 20s before have DS
I am plagued constantly in daily life by dopamine chasing, guilt and a brain that never shuts up. Topped off nicely with over compensating at things like work and anything to do with my son