User blog comment:DiegoAnime3000/Just wanted to point this out./@comment-24631732-20140801084156/@comment-96.254.157.84-20140801085657

We don't know the historys of the other teachers. They might not have been teachers when Cynder was there - Glynda doesn't look that much older than her.

The fact that he made those mistakes would be more of a reason to keep Cinder close to him, to make sure she doesn't make any sudden moves.