First, stop digging.

In addition to being a gross violation of privacy, drug testing high school students doesn't slow down their drug use one bit.

[T]he new federally financed study of 76,000 students nationwide, by far the largest to date, found that drug use is just as common in schools with testing as in those without it.

"It suggests that there really isn't an impact from drug testing as practiced," Dr. Lloyd D. Johnston, a study researcher from the University of Michigan, said. "It's the kind of intervention that doesn't win the hearts and minds of children. I don't think it brings about any constructive changes in their attitudes about drugs or their belief in the dangers associated with using them."

The prevalence of drug use in schools that tested for drugs and those that did not was so similar that it surprised the researchers, who have been paid by the government to track student behavior for nearly 30 years and whose data on drug use is considered highly reliable.

[...]

The same pattern held for every other drug and grade level. Whether looking at marijuana or harder drugs like cocaine and heroin, or middle school pupils compared with high school students, the fact that their schools tested for drugs showed no signs of slowing their drug use.

Imagine that - kids behave just like adults and learn how to beat the tests. So these incredibly expensive programs that accomplish precisely nothing (not unlike the results-free D.A.R.E. program) and that administrators and school boards are petrified to axe will just keep right on eating up educational dollars that could be used for, say, teachers' salaries or library books or fixing crumbling buildings. Instead, a bunch of officeholders get to go home and run on the misbegotten notion that they were tough on drugs and helped clean up our schools. Lovely.