School district lawyer Matthew Wright told NPR's Nina Totenberg (read her report):
"With hindsight and with calm reflection, we can look back and say, 'OK, what kind of danger really was there on campus?' " Wright says. "But when you're on the ground making on-the-spot decisions, you don't have that luxury. School administrators are not pharmacologically trained in being able to assess the relative dangers any one drug might present, but what they are charged with is to make sure that students are kept safe from such threats of danger."
So school officials can't be expected to exercise any kind of professional judgment, instead they are duty bound to be suspicion following automatons, all in the name of keeping kids safe.
Unless of course you are the kid getting searched, in which case the fact that you are an honor student who has never been in trouble at school only means that you are a criminal who hasn't been caught yet, whose right to privacy must yield in the face of the prime directive to keep everyone safe (huh).
In its brief, the school says the fact that Redding was an honors student who had never been in trouble before is not evidence of good conduct, but only evidence that she had never been caught.
The school views itself as a protector of its students' health and safety, which includes protecting students from both illegal and over-the-counter drugs. From the school's viewpoint, any suspicion that a student possesses drugs may be justification for a strip search.
Read chapter seven of my Governing through Crime for a fuller treatment of schools.
On the culture of control, See David Garland, The Culture of Control (2001)