The study described in this article is part of a broader research developed by the Project ESSA-Socio-logical Studies of the Classroom-whose main aim is to find out pedagogic practices more appropriate to all children. The study is mainly based on Bernstein's theory (1977, 1990; Domingos et al., 1986) and uses his concept of code as instrument of analysis. It intends to analyze the relation between general coding orientation and school achievement of socially differentiated children (social class, race, gender). It also intends to study the influence of differential modalities of school pedagogic practice on children's coding orientation. The results show that there is a mutual influence of family and school factors on students' coding orientation and science achievement. Specific characteristics of a pedagogic practice seem to be favourable to the development of the elaborated coding orientation required by the school.