This article examines the impact of class size on literacy skills and on literacy interest in beginning readers from zones with specific educational needs in France. The data came from an experiment involving first graders in which teachers and pupils were randomly assigned to the different class types (small classes of 10-12 pupils vs. regular classes of 20-25 pupils). Globally, the findings reveal that class size has a (small) impact on the two basic literacy skills, reading (word recognition task) and spelling (word production task). Children with high literacy interest made more progress than children with low literacy interest. The analysis also explores the effect of four factors--early schooling, age, first language and socio-economic status--on the same type of literacy skills as above. Smaller classes most specifically improved performances in two types of population: children whose first language is French and children from intermediate and average socio-economic brackets. This means, in contrast, that neither the children from the most disadvantaged backgrounds nor the children whose first language was not French benefited from the use of smaller first grade classes. Data in this experiment are examined in the light of studies on the connections between class size, classroom procedures and pupils' engagement.