Objectives: This study had a double goal: (i) analyzing the beliefs, attitudes and behaviors of Portuguese adolescents regarding trans and gender diverse people; and (ii) validating the short version of the Genderism and Transphobia Scale. Methods: A sample of 1,005 Portuguese adolescents aged between 13 and 18 years took part in the study. Results: Results indicated that boys exhibited more negative attitudes toward trans and gender diverse people than girls did, and girls exhibited more favorable attitudes toward trans women and gender diverse men than toward trans men and gender diverse women. The bidimensional structure of the scale was confirmed. Conclusion: These results highlight the close relationship between beliefs that reaffirm gender norms and mark the limits of the heterosexual matrix, transphobic attitudes and gender bashing. They are discussed in the context of a queer educational practice.