Suddenly All Might himself smashes the door open, his iconic loud laugh is heard as he proudly jumps into the classroom, hiding the fact he only has a few hours until he reverts back into his weaker form "I AM HERE!! Entering the classroom!!"

Class 1A squeals, specifically the girls

Midoriya stares at All Might with awe and surprise, he had no idea All Might would be teaching a class, its more awkward considering hes All Might's successor

Kirishima glances at All Might, squeaking before looking at Izuku, the guy he sits next to "I didnt know he was a teacher! Thats awesome!"

Midoriya nods twice and smiles, his excitement evident. It subtle but there, All Might definitely keeps an extra eye on Izuku

"Welcome to hero studies! I will be assisting you during spas and combat lessons to grip better control over your quirks." All Might winks and puts his thumbs up at the class