This study evaluates the effectiveness of a dialogic reading picture book intervention on preschoolers' repeating patterning ability. Ninety-four children age 4 years 1 month to 6 years 8 months (M[subscript age] = 5 years 0 months) were randomly assigned to intervention (n = 46) or active control (n = 48) conditions. Well-trained university and college students read two researcher-designed picture books five times each over 3 weeks (i.e., 10 reading sessions) to small groups of three to five children. In the intervention condition, repeating patterns were present in the text and the illustrations, and the dialogic reading questions elicited patterning interactions. In the control condition, there were no references to patterns and the dialogic reading questions focused on content other than patterns or mathematics. A repeating patterning measure (including extending, generalizing, identifying the unit) and a numerical measure (including counting, number recognition, number order) were administered at pretest and at posttest. At posttest, differences in repeating patterning between both conditions were not significant when controlling for pretest performance and receptive vocabulary, despite a small effect size. When further exploring the differences on each of the patterning tasks separately, the intervention group outperformed the control group on extending but not on generalizing or unit identification. There were no significant transfer effects on the numerical measure. Overall, this study shows that reading picture books specially designed around patterning skills can stimulate young children's ability to extend repeating patterns. Picture books are a promising tool to support children's patterning ability, because they are easy to implement in several early learning environments.