No. I'm a special ed teacher and have seen dozens of kids w/ ADHD, and I would never presume to tell a parent their kid has ADHD. Even though I am quite experienced w/ teaching children w/ disabilities, I am not qualified to diagnose. And I would NEVER presume.

I wouldn't say anything, but I can see how in some circumstances an honest conversation between good friends would be desired. I think my son's best friend is ADHD. While it's none of my business and I actually don't give a crap, I'd appreciate some honesty from my friend because 1) I've been forthcoming about my own son's ADHD, 2) we are good friends and 3) her son has done some pretty serious things under my care and an explanation would help me make sense of it. Still, it is not my place to say anything nor will I.

I have said something to my best friend, because:
1. we are very close
2. my child has been diagnosed with severe inattentive ADHD
3. her child, whom I have cared in various setting, exhibits the same symptoms.

But in other circumstances, just be mindful and delicate in your language, and be aware that your friend might be offended, even if it turns out you're right!