Complex sentence: Five years ago, he was a strict teacher in an engineering school, well known for changing a lot of delinquents in the school for the better, but at Tomoya's school, his skill is not needed due to the prestigious image of the school.
Split into simpler sentences: Five years ago, he was a strict teacher in an engineering school being well known for delinquents. He changed a lot of delinquents in the engineering school for the better, but at Tomoya's school, his skill is not needed due to the prestigious image of the school.