Kyoukasho ni Nai!

Both feature teacher-student relationships especially with problem students. The difference being GTO is a strong teacher and focused on delinquents and getting along generally with students. Kyoukasho ni Nai (Very Private Lesson) is more about a wimpy teacher being played by a problem student who happens to be a Yakuza boss' daughter. KNN is more ecchi, but only two OVA episodes were made despite 18 volumes in the manga. 

Similar relationship teacher and student teacher and student living together similar ecchi scenes both teachers have same comportament differences aya is rich and hase is poor 

Similar themes of a male teacher living with a female student while trying to keep it a secret from everyone else out of fear of losing his job.The female lead wants to have sexual contact with the teacher despite her father forbidding any sexual contact . In Very Private lesson there are some differences from Okusama wa Joshikousei like the main male lead is not married to the female lead. The male lead is actually interested in a fellow female teacher, there is some action, more comedy and a little bit ecchi.