This paper discusses ESSCOTS systems -- Educational Support Systems based on Commercial-Off-The-Shelf software. ESSCOTS are developed by selecting an existing commercial software product (the "COTS") around which the authors build an education software environment (the "ESS"). The authors' initial experiences indicate that the ESSCOTS approach to developing educational software has several advantages over developing systems from scratch. The authors begin with an overview of a specific ESSCOTS system based on ARC/INFO, a geographical information system. The authors then describe the formative results of piloting this system with middle- and high-school students, focusing on some especially impressive inquiries that the system enabled. The second half of the paper discusses more broadly the potential benefits of developing educational software as ESSCOTS rather than "from scratch." The authors argue that ESSCOTS can suggest project-based curricula and curriculum reform ideas, stimulate connections between classrooms and work, and profitably couple science, business, and education. The authors also suggest that ESSCOTS can provide important dual-use applications of technology, consistent with the Technology Reinvestment Project.