Constitutionally, random testing has already been tested and accepted as legal, for most any after-school or school based activity under Earls.
Privacy rights of public school students are diminished, and are not the same as the man on the street. First, minors are not full citizens. They do not have the same rights as adults, but they also are not subject to the same responsibilities (they aren’t automatically tried as adults, and they can’t be held responsible for contractual obligations if they don’t want to be). Second, public schools are government entities, and therefore the students are in the custody of the government to a certain extent while in school. Therefore, the school has a duty to protect the students from certain influences, as well as protect students from each other, as any harm that comes to them they could be responsible for in the end (the parents can sue the school).
Those that are involved in after-school programs are in the care of the school longer, or to a greater degree. They travel to other schools to preform, compete, etc. This adds an additional liability for the school, and therefore, if the student wants to take advantage of the program, they have the choice to do so under the rules the school sets forward to protect itself.
This isn’t about making sure that the students are taking preformance-enhancing drugs and therefore “cheating.” It’s about the school attempting to protect the children under its care to its best ability.
The fact that these are minors shows that it is, in this case, limited to a particular group that has historically been a protected, and paternalized, class. This doesn’t suggest danger in a “police state” form. Personally, I think it’s too far to have someone listening outside the door. However, the testing itself is not an affront, by itself, to our rights…and it is firmly supportable under the law as it has been throughout history and as we currently consider it in relation to children.