Ansatsu Kyoushitsu, Rokudenashi Majutsu Koushi to Akashic Records Recommendations
1. Both series are teacher related.
2. Both series teach a class which aren't looked up by others.
3. Both classes got a lot better after being taught by the teacher.
Both involve an unique op teacher, who has an unknown past (in both the past is explained after some time and the pasts are pretty similar).
His students hate him first, but after some time they begin to like him.