My son took clonidine for a while for his tics and hyperactivity. It helped a great deal with those issues, but does not help with the concentration/attention problems.
If you do go the clonidine route, I highly recommend the patch form over taking it orally. Orally is fairly short-acting and so the kids have alot more problems with sleepiness after they take it and, then, rebound hyperactivity as it wears off. The patch worked consistently well for about 4-5 days for us (as opposed to the 7 that is advertised).
Apparently, a lot of children have trouble with skin irritation from the patch form but it was never a problem for my son. The problem we did have with it was constipation. I didn't realize that it was the clonidine causing it until we stopped the clonidine.
Hope this helps....