In this paper, single-sex and coeducational schools are compared in terms of pupils' perceptions of disciplinary and academic climates. Use was made of data from 68 secondary schools in Flanders (Belgium). Of these schools, 25 were mixed and 43 were single-sex (21 girls, and 22 boys, schools). Respondents were third-year students: 3370 girls and 3057 boys, aged 14 and 15 years. A multilevel analysis (HLM) was performed, taking into account the effect of parental socioeconomic status, grade point average (GPA), curriculum-enrolment, parental support and school mean SES. The results mainly indicate that girls in single-sex schools, as opposed to girls in coeducational schools, perceive their schools as placing stronger emphasis on order and control. With regard to perception of academic standards, no differences between mixed and single-sex schools appeared. (Contains 2 tables.)