This study extends previous environmental education research on gender differences by investigating the gender gap between boys' and girls' sustainability consciousness. The issue of whether the gender gap in environmental education can be identified also in sustainability education is addressed. It has been suggested that Education for Sustainable Development (ESD) is a teaching approach that could play a key role in diminishing the gender gap. However, the possible gender-specific effect of an ESD-oriented teaching approach is empirically untested. A survey instrument was used to detect the hypothesized gender gap in students' sustainability consciousness on a sample of 2,413 Swedish students aged 12-19. Findings reveal a gender gap in students' sustainability consciousness. The gender gap increases throughout the age span and is amplified in ESD-oriented schools.