KYUUSAI NO KYOUSHITSU

Kyuusai no Kyoushitsu summary:

Makoto Noda, a run-of-the-mill Japanese teacher, endures ridicule from his students while struggling to manage a classroom on the verge of collapse. On a fateful day, a misunderstanding leads to a slap from a PE teacher, causing him to hit his head on the corner of a desk and lose consciousness. When he awakens, he finds himself facing a mysterious window. As he completes them, his real-life stats improve and he also acquires special items...! With his newfound ability, can Noda save the failing school from ruin?