S.B.
I used to be a HS teacher & I can honestly tell you that I knew quiet a few children who benefited greatly from being on medication. I don't know what medicine they were on, but it definitely made a difference.
I would talk with his daycare teachers & ask them if they've noticed a difference. I would talk to them right away and let them know you are trying medicine & ask them to specifically watch him for the next few days to see if anything changes. Everyday when you pick him up, ask them how his day went & if there were any improvements. Ask them if the morning was better than the afternoon. Ask them if they noticed when his "best", most focused time of day was. Write all of this down as soon as you get home to see if there is a pattern. If every day he has great mornings, but not so great afternoons, then you may need to add a second dose.
Also, you should be able to notice differences over the weekend. Good luck. And you have no reason to feel guilty. You've tried the other options, they didn't work. This might make his life much easier, you should be proud of trying it.