I hope your son will deal with ADHD well. One of my best friends with ADHD is doing his PhD in Engineering. So, it will be difficult, but I believe your son will overcome this.
If you like you can read the following posts. I have ADD without hyperactivity, but impulsivity and lack of concentration are big problems for me.
https://steemit.com/.../warning-you-might-have-had-attention-deficit-disorder -add-without-hyperactivity-though-you-are-an-adult
https://steemit.com/.../how-to-deal-with-adult-attention-deficit-disorder-add- without-hyperactivity-restructuring-your-mind