I wonder about this type of thing a lot when I think of my experience in school. a lot of the material they taught me in lower and middle school was just wrong. not like subtly wrong, but blatantly incorrect in a way that would be obvious to any undergrad major in that subject (which schoolteachers often are). I'm sure the teachers must have realized too. why spend so much time teaching stuff that needs to be unlearned as early as high school?
the best example I can think of right now is the answer to "why is the sky blue?". my lower school science teacher told us it was reflecting the ocean. I'm sure she realized this answer didn't make any sense, but that's what she taught us. I don't expect teachers to try to explain raleigh scattering to a group of third graders, but wouldn't it be better just not to explain it at all?