While school culture is often presented as a potential predictor of the school mean achievement in the school effectiveness and improvement literature (Hargreaves, 1995 ; Heck & Marcoulidès, 1996), only few studies have actually explored the impact of school culture on school effectiveness. Moreover, the rare studies on the impact of school culture (for example Gaziel, 2001) focused only on members' average response and neglected the possibility that a meaningful increment tothe prediction of organizational effectiveness might be provided by the variance in members' culture perceptions. The first objective of this paper is to discuss the meaning of such a conceptualization of the school culture and to propose a distinction between the values (measured as the mean beliefs) and the strength (measured as the variance in the team beliefs) of the school culture. The second objective is to test the impact of four cultural scales on mathematics and language achievement (academic emphasis, disciplinary emphasis, collegiality and innovation) in a representative sample of 52 schools (N = 2164). Main effects of the cultural mean and variance perceptions, but also the interaction effects are presented.The sample consists of 2164 students nested in 52 schools from the French community of Belgium. The sample is representative of the school composition's distribution into the population. Neither the mean nor the variance of the sample differ from the mean and the sample of the schools' population from French-speaking Belgium.Since students are nested within schools, a multi-level analysis is applied (HLM 6.2, Bryk & Raudenbush). First, a null model (without explanatory variables) is fitted to provide estimates of the variance components at each level. Second, individual parameters are added to the model (prior achievement, sociocultural capital and sex). Third, mean cultural scales, variance perceptions and interactions terms are succesively entered into the model as level-2 variables. All explanatory variables are centered around their grand mean, in order to facilitate computation and interpretation. Interaction variables are the products of the centered mean and variance perceptions for each cultural scale.First we expect all the four cultural scales to predict significantly the school mean achievement. Second we predict that the between-schools variance will also be explained by the interaction terms, meaning that when a cultural value is highly shared by the teachers' team, its impact on the school effectiveness is stronger.Heck, R & Marcoulides, G. (1996). School culture and performance: Testing the invariance of an organizational model. School Effectiveness and School Improvement, 7(1), 76-95. Hargreaves, D. (1995). School culture, school effectiveness and school improvement. School Effectiveness and School Improvement, 6(1), 23-46.Dumay, X. & Dupriez, V. (in press). Accounting for class effect using TIMMS 2003 8th grade database: net effect of group composition, net effect of class process and joint effect. School Effectiveness and School Improvement.Dumay, X. & Dupriez, V. (2005), Effet établissement : quelles relations entre composition et processus internes ?, Mesure et évaluation en éducation, 28(2), 67-92.