Definitely a classic! Deeply skeeved by the behavior of the teacher, but otherwise a really cute story with really cute MCs. A little non-eventful as a standalone, but there are sequels/follow up vignettes. The trouble is they're hard to find because so many of the author's characters look like Rihito and I have no idea what the actual order is. I may buy these, but in the meantime just look up by author and flounder, I guess!
Sequels: Setsugyousei ; Occupation to Beloved
Spin-off with creepy teacher and a different high school boy: Sora to Hara
Doukyuusei (NAKAMURA Asumiko)