A substitute teacher changes the lives of the slum children in his class.

West Indian Mark Thackeray, a qualified engineer, is unable to find employment in his chosen field and takes a position as a high school teacher in London's East End slum. He finds himself confronted by a rough, unruly bunch of teenagers who have forced several of his predecessors to resign. Aware that the youngsters are basically decent and that their crude behavior and language simply reflect an indifferent upbringing, he decides to deal with their rebelliousness by treating them as adults. Discarding all the old educational rules, he throws away the class textbooks, takes the students to museums, and talks to them about marriage, rebellion, sex, and the society they will enter in a few months. Shocked by their sudden treatment as equals, they abandon their hostility toward teachers and model themselves along the standards of conduct and decency Thackeray establishes. Inevitably, the teacher suffers a few setbacks: one of the girls, Pamela Dare, imagines herself to be in love with him; the class ringleader, Denham, must be outboxed in gym class before there can be mutual respect; and the unorthodox teaching methods are sometimes ridiculed by other faculty members. Thackeray's influence is so strong that the students defy local convention by attending the funeral of a classmate's mother, even though the student previously was ostracized because of his mixed parentage. When it is time for their senior dance, the students have evolved into attractive young adults ready and eager to face the world. The dancing is interrupted when the class expresses its gratitude by having Barbara Pegg sing a song dedicated to their favorite teacher. His eyes filled with tears, Thackeray returns to his classroom and stares at a letter offering him an engineering job. As he tears it up, he meets two ill-mannered and rebellious youngsters who threaten to disrupt his class next term.