My favorite teacher student romance anime would be
1) I My ME Strawberry Eggs:
Hibiki is a real teacher who cared a lot for his students, and he never tried to make any advances with his female students nor took advantage of their vulnerabilities, although in Fuuko's case, Hibiki made a great deal of effort holding back his feelings for Fuuko.But that was his honest feelings, not lust and he was trying to deny his feelings to the point of lying to himself but in the end, he gradually realized he liked Fuuko, even though he knew it was wrong. At least He cared for Fuuko enough that he encouraged her to try her best.
2) Card Captor Sakura:
Yes, I know Rika-chan is too young for him. But if she was of lergal age, I would love to see Rika together with Terada-sensei. Rika and Terada's love for each other is purely innocent. If Terada was evil and wanted her body only, he would have hurt Rika. But He would never harm a hair on her head. Nor would he take advantage of Rika's trust. He was very nice and takes care of his students especially Rika. Love is love. Age doesn't matter. How can they not be meant to be together? Terada and Rika have such wonderful mutual rapport in spite of their age gap. Terada-sensei is an intelligent, mature, dependable, considerable and serious teacher. Also, Rika-chan is a bright, eager, studious, thoughtful and very precocious girl who excels at many subjects. A perfect teacher and perfect student. It is a good combination.