This article presents the results of a study carried out with the aim to: (1) analyze secondary school students' and their teachers' ideal representations of classroom justice, (2) deepen the topic of students' sense of injustice, and (3) explore the links between students' perceived injustice and their psychological engagement in school, measured on different aspects (identification with one's own class, learning motivation, dialogue with teachers). A questionnaire was distributed to 400 Italian secondary school students and their 79 teachers. Results show that the representations of ideal classroom justice refer to communication, principle of equality and principles of effort/need, and that the positions of teachers and students on these representations differ. Moreover, students report a rather diffuse and shared feeling of being treated in an unjust manner by their teachers, and this affects their psychological engagement in school. Results are commented on their theoretical, methodological and applicative implications.