Camporees are good opportunities for this. Choose a troop that you and your son both like. Sometimes you and your son can leave a troop visit with very different impressions of the troop. Troops vary greatly in size. Some boys are excited by a large troop, some are intimidated.
Some boys find a small troop boring, while others fine it comfortable and more personal.
It is nice if all of the boys in your den join the same troop, but encourage each to make his own decision. A boy will drop out of a troop where he is not comfortable, even if his friends are there. There should be an even distribution of ages and ranks. A new Scout probably would not be comfortable in a troop consisting mostly of older boys. On the other hand, if most of the boys are young, there may not be adequate leadership.