Re: Best snare heads for sharp/cutting sound?
Don't know if your son is taking lessons but learning how to do a consistent rim shot would help quite a bit.
Often times I feel players are trying to get a rim shotted snare sound out of hitting a batter dead center. When you use a rim shot (hitting the rim and the head simultaneously) you introduce another measure of cut that doesn't have to be hit hard to project (although using a rim shot and hitting hard happens often too.)
If he hasn't done a rim shot before he'll need to have someone show him how and then practice it over and over until it becomes natural.
As others have said a brass or even steel drum will give more cut. Steel cuts especially well except I personally don't care for the sound of steel snares on most drum models. Brass gives a sweeter sound with more presence than a wood snare. I have maple bronze and Ludalloy (aluminum based) snares and like all of them quite a bit. I would recommend bronze except that it's a warmer sound than brass. Bronze snares are often described as having the characteristics of wood and metal which is why I have (2). :)
The above and the single ply heads others have recommended should help,