[EricH]

I haven't been on a team with someone with ADD that I know about...

It might be best to figure out how to make sure that the medication is taken each and every day. For that, you want to sit down with both the student and the student's parents. Explain the situation, and that the best way to reduce the effects is to ensure that the medicine is taken. Work with the parents to find a way to do that, as they know their teenager much better than you do.

I would also say that if I was a parent I would want to know that any medication my child was on was being skipped now and again. Then it's time for a parent-child discussion on responsibility and the purpose of said medication...

Because this is a fairly regular occurrence, you may be able to figure out why it's happening, too. Say it's usually on a Wednesday, just for purposes of explanation. Maybe the student has something Tuesday night that causes them to stay up late, then has something during zero period, and is rushed between waking up and leaving for school. That would be something that the parents might know about, but you wouldn't necessarily. If they know there's a problem, they can deal with it better than you can.

Definitely bring the parents in while you work on this.