Prior research shows that shared book reading promotes preschoolers´ language and literacy skills. However, little is known about the potential role of books´ features –e.g., wordless picture books vs. books with text– in children and teachers´ spontaneous language production. In this study, we transcribed verbal interactions of thirteen Colombian teachers reading to groups of preschooler students (aged 43 to 55 months) during reading sessions in Spanish using wordless picture books (condition 1) and prototypical storybook with text (condition 2). Books were matched for page length, genre and theme. Using Computerized Language Analysis (CLAN), we found important differences in children and teachers´ spontaneous language production. Specifically, paired t-test comparisons revealed that in the wordless-picture-book condition: (a) children produced significantly more word tokens, word types, utterances and questions (all p´s < .05), and (b) teachers produced significantly more word tokens, questions and levels of instructional support (all p´s <.05).