At 11 I think my DS should be showering daily, he sweats during the night a fair bit and also is a very active child. It became a daily argument with him and then my DP decided that at 11 he is fine to shower every other day because he has not yet hit puberty 
My son is still a nightmare to get in the shower every other day, but at least it's not a daily argument.
However, I still think he should be showering each day.
How often does your preteen shower and do they do it without being asked to do so or have to be pushed?