This dissertation offers the first set of empirical studies to examine the differential impact of didactic instruction and playful learning practices on geometric shape knowledge. Previous research demonstrated that successful child-centered, guided play pedagogies are often characterized by two components: (a) dialogic inquiry, or exploratory talk with the teacher, and (b) physical engagement with the educational materials. Building on this conclusion, three studies examined how guided play promotes criterial learning of shapes. Experiment 1 examined whether guided play or didactic instruction techniques promote criterial learning of four geometric shapes compared to a control condition. Results suggested that children in both didactic and guided play conditions learn the criterial features; however, this equivalence was most evident for relatively easy, familiar shapes (e.g., circles). A trend suggested that guided play promoted superior criterial understanding when learning more complex, novel shapes (i.e., pentagons). Experiment 2 expands on the previous study by examining how exposure to enriched geometric curricular content (e.g., teaching with typical shape exemplars only vs. typical and atypical exemplars) augments shape learning in guided play. As hypothesized, children taught with a mix of typical and atypical exemplars showed superior criterial learning compared to those in taught with only typical exemplars. Experiment 3 further explores the factors that facilitate shape learning by comparing the effectiveness of guided play, enriched free-play, and didactic instruction on children’s criterial learning of two familiar shapes (triangles, rectangles) and two unfamiliar, complex shapes (pentagons, hexagons). As hypothesized, those who learned via guided play outperformed those who learned in didactic instruction who, in turn, outperformed those in enriched free play. In both didactic instruction and guided play, children’s shape concepts persisted over one week. The findings from these studies suggest (1) guided play promotes equal or better criterial learning than didactic instruction, (2) curricular content (shape experience) augments criterial learning in guided play and (3) dialogic inquiry may be a key mechanism underlying guided play. The current research not only has implications for enhancing the acquisition of abstract spatial concepts but also for understanding the mechanisms that foster playful learning.