This article presents the results of an RCT assessing the impact of a Shared Book Reading (SBR) intervention that targeted children aged 4 attending kindergarten. We selected a large, random sample of families living in the city of Paris and provided parents of treated classes with free books for children, information on the benefits of book reading and tips for effective reading practices. We measured book reading frequency and children's vocabulary before and after this intervention among treated and control children, and we found evidence of positive treatment effects on book reading frequency and on one of our two measures of receptive vocabulary. Moreover, we measured treatment impacts on this vocabulary measure at a 6-month follow-up and found that they were persistent. This light-touch intervention was particularly beneficial to male children, to children from families with low levels of education and from the most disadvantaged schools. Children from bilingual families benefited as much as their native counterparts.