This study examined the effects of an SLP-delivered whole-class interactive book reading intervention and a professional development program on children's self-initiated participation. Eleven kindergarten teachers and the children in their classes participated in this quasi-experimental study. They were filmed during book reading at pre- and post-intervention, and follow-up. Children's types of spontaneous comments appeared to be more diverse after the intervention, and the types that increased or emerged were consistent with the language targets of the interactive book reading. Nonparametric statistical tests were conducted. Significant changes were found in the number of hands raised by children to make a spontaneous comment and in the number of spontaneous comments after the intervention and at follow-up. Results for child-initiated interaction sequences were mitigated. This study invites school-based SLPs to foster children's self-initiated participation in their tier-1 intervention and to support teachers in using children's spontaneous comments to further scaffold children's learning.