It is quite popular to blame teachers for their students' intellectual choices. Of course, teachers may do a great job or a poor job. But students, it seems we sometimes forget, have free will.
Once upon a time there was a perfect Teacher. He taught many, but twelve were part of His inner circle for three years, not just in a classroom a few hours a week but walking and talking and absorbing his teachings every minute of every day.
Eleven of them abandoned Him in His worst moment.
But one had already betrayed Him utterly.
That one must have appeared to the rest to understand and go along with His teachings at least as well as they did; not one pointed his finger instantly at the one rebel they all knew so well when He said that one of them would betray Him. They all asked "Is it I?" Only the betrayer knew the answer.
If He hadn't been the perfect Teacher, the only One who could really read people's hearts despite their apparently compliant actions, He might have been deceived, too. He might have thought this one was learning and accepting His lessons, and been utterly surprised by his defection, his hatred.
It happens to teachers every day, breaking their hearts, making them wonder where they went wrong. Ordinary teachers surely did go wrong somewhere, but their wrongs may not have had anything to do with a student's defection from their teaching.
This whole teaching/learning enterprise is a two-way street. Even the perfect Teacher couldn't make His students all wholeheartedly accept His teachings. Why then do we expect imperfect human teachers to do better than He did? Why do we automatically blame them, especially when we don't or only barely know them, instead of considering that the student bears at least as much responsibility for his choices in response to the teaching, that he might have played along to get good grades in the classroom, or changed his ideas after graduation, or a bit of both?
When our students fail in life, we should indeed check ourselves -- did I do the best I could, as a teacher and a mentor? But when we know we did -- our best not precluding error, but not being error the student couldn't overcome with intelligence and good will -- then we needn't take responsibility, only grieve for the lost sheep.