This study investigated the links between the teaching practices of primary school teachers (n = 200) who were observed while presenting a new text to their first year classes, and the student achievement levels in those classes. The teaching practices are specifically concerned with the way the teachers supported and encouraged students’ activities during verbal interactions. Two different populations were observed: classes of first year students with a reduced teacher–student ratio (about ten students per class) and classes with a normal teacher–student ratio (between 20 and 25 students per class). We found that the average level of student achievement in the reduced size classes was higher than in the standard size classes but that teaching practices differed only at precise periods of group or individual introduction to new reading texts. In these periods, we found links between teaching practices and student achievement.