Summary This study investigates the relationship between chronic sleep reduction, functioning at school and school achievement of boys and girls. To establish individual consequences of chronic sleep reduction (tiredness, sleepiness, loss of energy and emotional instability) the Chronic Sleep Reduction Questionnaire has been developed. A total of 436 children (210 boys, 214 girls, 2 missing; mean age = 11 years and 5 months) from the seventh and eight grades of 12 elementary schools participated in this study. The inter-item reliability (Cronbach’s alpha = 0.84) and test–retest reliability (r = 0.78) of the Chronic Sleep Reduction Questionnaire were satisfactory. The construct validity of the questionnaire as measured by a confirmative factor analysis was acceptable as well (CMIN/DF = 1.49; CFI = 0.94; RMSEA = 0.034). Cronbach’s alpha’s of the scales measuring functioning at school (teacher’s influence, self-image as pupil, and achievement motivation) were 0.69, 0.86 and 0.79. School achievement was based on self-reported marks concerning six school subjects. To test the models concerning the relations of chronic sleep reduction, functioning at school, and school achievement, the covariance matrix of these variables were analysed by means of structural equation modelling. To test for differences between boys and girls a multi-group model is used. The models representing the relations between chronic sleep reduction – school achievement and chronic sleep reduction – functioning at school – school achievement fitted the data quite well. The impact of chronic sleep reduction on school achievement and functioning at school appeared to be different for boys and girls. Based on the results of this study, it may be concluded that chronic sleep reduction may affect school achievement directly and indirectly via functioning at school, with worse school marks as a consequence.