Its no different than discussing the list of possibilities of why someone wasn’t accepted to a certain school, or why a potential shidduch didn’t work out. I’ve also heard these discussions and aside from it being pure lashon hara they only have negative effects. I was once in a smaller school (where teachers know all the students, even if they never taught them) where a teacher (not this childs teacher) said, “oh, so and so? shes so weird”. I know of another child who ended up with a bad reputation just from shmoozing his teachers did.
If anyone is in a position to institute some sort of shmiras halashon program in the teachers lounge in their school, it can help even one child, and yes, thats a big deal.