Looks likes there are only three students in that class. All the others are faceless mute mobs.
And I can't help but notice that the students "reacting" to her teachings were all female and pretty level headed.
I can see why why she didn't use boys: they would either look embarrassed, horny or being all like "hur hur hur... sex, condoms...", leering at the girls, or virtually elbowing each other, if she was to be realistic.
Obviously, author forgot (or choose to ignore), what a class full of teens is.