Twenty-thousand dollars could do a lot for a typical cash-strapped school district. You could renovate a classroom, or hire a part-time teacher's aide, or buy some computers or a whole bunch of text books.

The school district in Carroll County Georgia -- about 25 miles west of Atlanta -- has $20,000 to spend, but it won't be on any of those things. Instead, they're implementing a random drug testing program for their public high school students. They plan to test up to 80 students each month, according to WSB-TV in Atlanta. With school drug tests costing about $24 a pop, according to Dr. Sharon Levy of the American Academy of Pediatrics, that works out to about $20,000 per year.

According to the Centers for Disease Control & Prevention, about 18 percent of public high schools -- nearly 1 in 5 -- have mandatory drug testing policies like the one Carroll County adopted. Like most of these programs, Carroll County's only applies to athletes, students participating in other extracurricular activities (like marching band), and students who drive to school.

It may seem odd that a school can require your kid to get tested simply for joining, say, the chess club. But the Supreme Court upheld the constitutionality of such programs in 2002. "We find that testing students who participate in extracurricular activities is a reasonably effective means of addressing the school district’s legitimate concerns in preventing, deterring and detecting drug use,” Clarence Thomas wrote for the 5-4 majority.

But schools are increasingly pushing further. For instance, a nationally-representative survey of 1,300 school districts found that among the districts with drug testing programs, 28 percent randomly tested all students -- not just ones participating in after-school programs. These schools are opening themselves up to a legal challenge

But in the years since the Supreme Court ruling, numerous studies have shown little evidence of effectiveness among these programs. To wit:

  • A 2013 study looked at 14 years of data on student drug use and found that school drug testing was associated with "moderately lower marijuana use," but increased use of other, more dangerous illicit drugs.
  • A 2014 study concluded that drug testing was "was not associated with changes in substance use."
  • A 2013 study comparing drug use rates among schools with and without drug testing programs found some short-term deterrent effect among students who were tested, but no effects among students who weren't tested, and no long-term effects on either drug use or intention to use drugs in the future.

More to the point, school drug programs don't test for the one drug that is most favored by high school students, and which is also the most hazardous to their health: alcohol. The tests also carry a number of significant negative consequences in and of themselves: students subject to testing may be less likely to participate in extracurricular activities. The tests may violate students' privacy by making their personal medications known to school administrators. And they may subject students to disciplinary action, like harsh long-term suspensions and expulsions, that harm their academic prospects.

For all of these reasons, the American Academy of Pediatrics recently came out against the widespread adoption of drug testing in schools. "The AAP supports effective substance abuse services in schools but opposes widespread implementation of drug testing as a means of achieving substance abuse intervention goals because of the lack of evidence for its effectiveness," they wrote.

The National Institutes on Drug Abuse says that "because of the conflicting findings on student drug testing, more research is needed," and that "drug testing should never be undertaken as a stand-alone response to a drug problem."

Despite the research and the guidance of experts, the proportion of public high schools with random drug testing programs has risen from 14 percent in 2006 to 18 percent in 2012, according to the CDC. Schools in Ohio, New Jersey, South Carolina, Alabama, and Wyoming are currently considering mandatory drug testing programs.

One last number for you: school drug tests tend to not yield a lot of positive results. Sharon Levy of the AAP estimates that it costs $3,000 for each positive test, or about 1 positive for every 125 students tested. That means that Carroll County, Georgia's $20,000 investment will turn up about 6 student drug users -- 7 if they're lucky.