A US Department of Education research report released Wednesday suggests that mandatory random drug testing of high school students has a small positive impact in reducing past-month drug use, but has little effect on teens' intentions to use drugs in the future. Nor, the study found, is there any indication that drug testing of athletes and students involved in extracurricular activities has any spillover effect on students not involved in such programs.

The Department of Education study surveyed students at 36 high schools that received federal grants to implement drug testing programs. Half the schools had already implemented drug testing, while the other half held off on it until after the study period.

Under a pair of US Supreme Court decisions, school districts were given the okay first to subject student athletes to mandatory random drug tests and later to expand the testable population to include students who engaged in extracurricular activities. Under a federal grant program in place since 2003, the number of school districts subjecting students to the privacy-invading drug tests has increased from about 5% at the beginning of the decade to 14% now.

But the Department of Education study suggests student drug testing has little lasting positive impact. The brightest news for drug testing advocates is that among students in extracurricular activities in schools with such programs, only 16.5% reported past month drug use, compared to 21.9% in schools without drug testing regimes. Also, drug testing programs did not appear to inhibit students from participating in extracurricular activities.

While the presence of drug testing slightly reduced self-reported drug use among students engaged in extracurricular activities, the study found no impact on students not involved in extracurricular activities. In both drug testing and non-drug testing schools, 36% of those students reported using a drug within the past month.

Nor did the presence of drug testing programs have any impact on teens' plans to use drugs in the future. According to the study, 34% of students covered by drug testing reported they "probably will" or "definitely will" use drugs in the next year, compared to 33% of comparable students in schools without drug testing.

The obvious conclusion seems to be that if schools want an effective means of reducing student drug use, mandatory random drug testing isn't it -- it's achieved only modest and temporary reductions in teen drug use, and limited to those achieving teens who least need the help.