Sparkly – While there are going to be teachers who rub their students the wrong way, there are usually underlying factors that cause them to go off the derech. You can’t blame it total on the teachers, the home and outside environment play a major part in it. Back 50 years ago there were a few Rabbis such as R’ Avigdor Miller who would answer any questions no matter how anti religious it was. His book Rejoice O Youth should be required reading as it answers many of the questions that people going off the derech ask.
Avi K: You do realize that by wondering how many Kosher Eidim are left, you re saying that the majority of witnesses are not kosher. Jewish Weddings would be invalid due to non kosher Eidim as only Kosher Eidim make the wedding valid. The only explanation is that he repents prior to or at least as he is going up to be a witness.