Geospatially enabled learning technologies may enhance Earth science learning by placing emphasis on geographic space, visualization, scale, representation, and geospatial thinking and reasoning (GTR) skills. This study examined if and how a series of Web geographic information system investigations that the researchers developed improved urban middle-school learners' GTR skills and their understanding of tectonics concepts. Paired-sample t tests for analyses of tectonics content knowledge and GTR achievement measures revealed statistically significant gains from pretest to posttest (p < 0.001) with large effect sizes. The findings provide support that GTR related to tectonics can be learned with appropriately designed learning activities using Web-based geographic information systems.