I wonder what the actual message is compared to what gets back to the parent. Are teachers really saying "Don't use wikipedia" full stop, then turning around and accepting any other webpage as a scholarly source? That seems really unlikely.
At worst, wikipedia is a tertiary source. I'm surprised I had to deal with this in college, but the teacher in one of my classes, after we submitted our first papers, felt the need to break this down and explain how to use wikipedia and properly cite sources in this context. I'm sure some kids turned off their ears after the beginning of that lecture...
It seems entirely apiece with how a rule begins ("Don't cite tertiary sources like encyclopedias, Wikipedia is an encyclopedia, so don't cite Wikipedia") and then gets simplified to the point of uselessness ("Don't cite Wikipedia", then finally "Don't use Wikipedia") and then generates its own inverse rule ("If it's not Wikipedia, you can use it").
At each stage the why gets shaved off and then people come up with their own reverse-engineered explanations ("Don't use Wikipedia because it's edited all the time by randos, so it's less reliable than the other stuff you'll find online").
You can see this with, eg, p-values- people learn the rule "A p-value measures the probability of obtaining the observed results, assuming that the null hypothesis is true." which becomes "a low p-value means we should reject the null hypothesis" becomes "a p-value is the probability the null hypothesis is true" (the inverse).
At worst, wikipedia is a tertiary source. I'm surprised I had to deal with this in college, but the teacher in one of my classes, after we submitted our first papers, felt the need to break this down and explain how to use wikipedia and properly cite sources in this context. I'm sure some kids turned off their ears after the beginning of that lecture...