Spatial skills support STEM learning and achievement. However, children from low-socioeconomic (SES) backgrounds typically lag behind their middle- and high-SES peers. We asked whether a digital educational app--designed to mirror an already successful, spatial assembly training program using concrete materials--would be as effective for facilitating spatial skills in under-resourced preschoolers as the concrete materials. Three-year-olds (N = 61) from under-resourced backgrounds were randomly assigned to a business-as-usual control group or to receive 5 weeks of spatial training using either concrete, tangible materials or a digital app on a tablet. The spatial puzzles used were an extension of items from the Test of Spatial Assembly (TOSA). Preschoolers were pretested and posttested on new two-dimensional (2D) TOSA trials. Results indicate that both concrete and digital spatial training increased performance on the 2D-TOSA compared to the control group. The two trainings did not statistically differ from one another suggesting that educational spatial apps may be one route to providing early foundational skills to children from under-resourced backgrounds.