This is a priority one!
Onegai Teacher was one of the first anime I ever watched (and probably the 1st non-Toonami series). A further note before I proceed with this review; this is one of the VERY few series in which I preferred the dubbed version to the subbed version. Though honestly, the voicing isn't that great either way. But to continue, this was the first anime that I truly got emotionally connected to the characters. All the characters in this series are fantastic. The two leads (Kei and Miss Kazami) are phenomenal; I see them as a very classic pairing. And the supplemental characters actually play a very vital role in the plot of the story. This is one of those series that certainly had enough content that with some filler material could have been in the 24 episode range as opposed to 12 (or 13 as I'll get to in a moment), which goes to show how fast-paced this series really is. Along with the very good serious ending Onegai Teacher has; it additionally has a wonderful little OVA that is from time to time referred to simply as episode 13. It really will enhance your viewing experience if you do watch the OVA immediately after watching episode 12. The OVA is a tremendous conglomeration of what has just transpired in episode 12 and the series as a whole. Also the OVA is very funny in contrast to the serious nature of the final few episodes of the "completed series." Overall, Onegai Teacher is brilliant and timeless, 9 out of 10.