First, since high school sports are considered by law extracurricular, participants do not have the right to sue if they fail a drug test as long as the expectations and consequences are clearly spelled out.
Second, many people have discussed testing the band etc. This is an invasion of privacy because band is considered by law as a curricular activity. In other words, band is an academic class and therefore participants cannot be drug tested.
Third, Greenville and Sullivan county schools are two that I know drug test or at least did at one time. Maybe someone in those systems can clue us in on its effectiveness.
Finally, any coach, parent, or administrator that opposes drug testing has missed the point of high school athletics. In my opinion, high school sports help teach student-athletes life skills, discipline, and teamwork. Drugs do not fit in these at all.