In this study, it was determined which factors influenced students' perceptions of their learning environment. Students' perceptions were measured with the What Is Happening In this Class questionnaire (WIHIC). Data were analysed for a large sample of US (California) middle school classes. Several variables were included in the study, such as student and teacher gender, student ethnic background and socio-economic background (SES), student age, but also class and school variables, such as class ethnic composition, class size and school SES. Hierarchical analyses of variance (multilevel analyses) were conducted to investigate separate and joint effects of these variables. In the presentation, we will report on effect sizes of these variables...