(Of course they should know this already, but as it applies to a classroom setting should still be discussed in class and thereby constitute a lesson in morals)
My point is that, as usual, it's not so easy to generalize and say 'no morals should be taught in school'.
Of course nobody wants the more nuanced morals taught as if there is a right or wrong (ex. abortion,gun rights,etc.etc) but SOME morals are appropriately discussed (and again, this constitutes a lesson) in a classroom setting.
Parents have the home and their places of worship to discuss other moral matters in a more deep and nuanced manner.