Different

I think the theme for the movie is to be unique. Before the teacher met them they were all the same kids and did what everyone thought and said. When they met Keating they instantly thought he was weird because they haven't met a teacher that taught like him. He was special and most of all unique. The students thrived off of this and wanted to be different like he was. The boys went off and did their own things, but they were doing things they would've never have done if they didn't learn to be unique and stand out.