Interesting High School Drug Testing Case

There’s a little case being considered in Fairbanks, Alaska that intrigues me.
The father of a High School student is suing over the district’s drug and alcohol policy. There are several issues involved, including the fact that the school had a policy of a 5-day suspension for failing a drug test, but a 90-day suspension for refusing to take one (they have since changed that policy).
The most interesting part, however, is the proper argument that urinalysis is an invalid measure.

One of the changes they are seeking is to prevent school officials from using a urine test to determine whether a student is intoxicated at school.æ When the assistant principal ordered Frey to take a urine test, the lawyers argued in a court filing, it amounted to an order for him to submit to an unreasonable search.
Because a urine test can detect a substance taken several days ago, the analysis does nothing to determine if a subject is currently intoxicated, they argued.
“There can be no legitimate dispute that the urinalysis requested could not prove whether Anthony Frey was, or was not, under the influence of some substance on the morning of May 22 at 7:35 a.m.,” attorney Don Logan wrote.

This is an extremely important point, and I haven’t heard of any other similar cases before.
It is important, not only from the perspective of school testing, but because of the push in many quarters for using urinalysis as proof of “drugged driving” (even though it gives absolutely no measure of current impairment).
The judge denied a request for a preliminary injunction, but “ruled that many of the Frey’s claims have merit and invited the attorneys to submit more briefs on the issues.” The Freys plan to continue to pursue the case.
I hope so, and I’m very curious to see what the results will be.
Any legal mavens want to weigh in? Can the government decide that a positive THC test will, in fact, be proof of intoxication, and legally define it as such (even though it’s not necessarily true)? How would the courts balance the constitutional rights with compelling government interests, if the action prescribed to achieve the government interests don’t actually provide data that is specifically pertinent?