There actually are, or were, two different programs.
The School Enrichment Program, for Grades 6-12 (normal CAP membership).
Junior Cadet Program for grade K-5.
When reviewing statistics, publicly available information from the schools participating, as
well as anecdotal conversations with members participating in those programs, membership
(or at least participation) drops off fairly precipitously in grades 9-12 at schools that
require the students to join JROTC as either an option to, or in place of CAP.
As we hear on a fairly regular basis, kids "forced" to wear a uniform all day, are not generally inclined
(on the mean) to be interested in wearing that uniform after school and on weekends, and just like at schools
where JROTC is a gym elective, don't tend to produce the quantities of invested cadets you'd think they would.
An issue we saw locally was that kids in the area who join the unit from the outside tend to be much more invested in
CAP in the way most of us understand it, vs. the kids from the actual school, as they were there because they
wanted to be, vs. mom and dad making them go during the day.
We also saw non-trivial issues where the charter-holder made it clear that the school itself was a public school
bound by the policies of the school board and charter, not CAP or the USAF, so while the students may well be
wearing USAF uniforms, grooming and courtesies were not enforced as required, resulting in just about the exact
situation you are imagining.
There also tends to be a very small contingent of senior members in relation to the large number of cadets,
because most activities are during school hours and are chaperoned or supervised by normal school staff.
CAPP 52-21 http://www.capmembers.com/media/cms/P052_021_0EA8D98F1D7A6.pdf
One unintended consequence of these units is the way they can drain resources from an otherwise
normally scaled wing. They generally have no pilots, few senior members, and move in force to various activities,
assuming they venture out much at all. In most wings, if a unit shows up with 20 or 30 members, they
become the majority at that activity - BTDT - imagine adding 100 cadets or more to the average encampment,
or trying to get that many flying. Assuming you can fly 6 cadets per day per plane, that's 16+ airplanes,
which results in either low o-ride percentages, or big blocks of time no one else can get near the planes.