Strattera - what dosage?

Our son just started on Strattera 1 week ago (10 mg/day) and today we started giving him 18 mg/day as the doctor told us to do.

We did see a lot of good effect only after a few days, haven`t heard anything from school yet so we have to see about that.

Is there a possibility he wont be needing 28 mg/day as the doc wants/calculated him to take? How will you notice if he is overdosed? Can you go back down in dosage then?

He has been on Concerta before and he then used 18 and 27 mg, I think he got the same effect on both 18 and 27 mg but more angry on 27 mg.  So I guess he dont need much medicin to get an effect, huh?