Our new standard for recruiting excellence in 17 and 18 year olds is the AAU, not high schools...(Many NBA coaches feel today's players don't get much fundamentals in the AAU programs; they're almost exclusively games, with little to no gym time for practice).
I'm not sure what the practice schedule is for older kids but my son (just entering 4th grade) has two or three two-hour practices a week, year round with his AAU team. In the Winter/Spring they have tournaments about every other weekend and in the Fall they play one league game a week. That's pretty typical for most AAU teams in my area (Washington DC).
The AAU programs I'm referring to are at the older levels - The guys running the teams usually have to pay for gym time out of their own pockets, and only book time for games. Dynamite what they're doing at 4th grade level, I remember playing on a uniformed team in 4th grade, it was a great experience, real helpful for the future.