Inferencing abilities are crucial to development of reading comprehension. However, few studies addressed those abilities in interventions promoting early literacy skills, especially in kindergartners. The aim of this study was to measure the efficacy of an interactive book-reading intervention targeting inferencing abilities, delivered by a school-based speech-language pathologist (SLP) in whole group kindergarten classes. Two hundred and forty-nine 5-year-old kindergartners from low socio-economic settings were quasi-randomly assigned to either one of the experimental groups (EG1 and EG2) or an active control group (CG). EG1 received a 7-week interactive book-reading intervention followed by a 7-week period where it was up to the teachers to implement aspects of the intervention in their teaching or not. EG2 received the 7-week interactive book-reading intervention only and the active control group received an initial workshop only. Three subtests targeting (1) causal inferences during book-reading, (2) causal inferences in a formal task, and (3) referential inferences in a formal task were performed at pre- and post-intervention assessments. There was a significant Time × Group interaction effect for the first subtest indicating an advantage for EG1 compared to CG over time. EG2 appeared as an intermediary group as its results were not different from EG1 and showing only a trend toward significance (p = 0.064) when compared to CG. There was no significant Time × Group interaction effect for the second subtest. A significant Time × Group interaction effect was present for the third subtest, EG1 and EG2 showing larger improvement than CG.