Sidney Poitier had three films released in 1967, in my opinion this was the best of them. "In the Heat of the Night" might have been more socially relevant when seen today, and "Guess Who's Coming to Dinner" might have been more conventionally entertaining, but "To Sir, With Love" was to me more intelligent, sensitive and emotional that the other two. I am amazed that Sidney was not nominated for the Oscar in 1967, but given his performances in all three films, it's obvious the voters were torn. Sidney Poitier had a year in 1967 that, due to the length of time it takes to make a film these days, may not be repeated now, that is 3 starring roles in three extremely profitable films which does not happen that quite often.
That said and done, I would like to say that is a film is excellent. Poitier gives an outstanding performance as Thackeray, the new school teacher, and the kids, for the most part, were really from the East End. Aided by an excellent supporting cast including Judy Geeson as Lulu which I believe, is Scottish; and Michael Des Barres "Gypsy," the kid with the ubiquitous sunglasses -- is of French aristocracy/English descent; otherwise, what you're seeing is what you get: kids from the East End.
True, the script and some of the cinematography are dated, but what do you expect? The film was made towards the end 1966 and released in 1967; in many ways, it was ahead of itself. The main point, however, is not cinematic technique but character development and storyline. "To Sir, With Love" does portray strong characters, and does develop in a logical, positive way resulting it to be an excellent film.