Interesting but it is my understanding that the follicle is the proper sample as externally exposed hair can absorb all sorts of material present in the atmosphere.
Why not just have the little chillren pee in a cup?
Much more effective sample, no?
Testing that checks hair samples for drug metabolites avoids false positives due to external exposure to the raw drug.
Additionally if the hair has been on your head for awhile it can give an approximate history of when drug use occurred.
I have no idea what the school is trying to prove but this is approaching police state tactics. It has no bearing on the current time frame or any indication what has happened during school time. Once this information is stored it will be available indefinitely to whoever can access the information. I’d pull my kids out or shave their heads and my some wigs.