Recent shifts in web map technology away from proprietary software and toward development on the Open Web Platform have increased the number and complexity of technical skills needed to do cartography on the Web. Web-based cartography curricula likewise must be adapted to prepare geography, cartography, and GIS students with the skills needed to make use of open source technology. This paper describes the design and evaluation of a novel curriculum for the laboratory component of a web mapping course offered by a university geography department. We drew from constructivist educational theory to create a scaffolded and spiralled lab curriculum that builds on prior understanding and progressively increases student independence and confidence. We evaluated the success of the new curriculum through an instructor log, student feedback on assignments, and an exit survey. The evaluation revealed significant growth in student abilities and confidence in the use of Open Web Platform-based mapping tools as a result of the curriculum scaffolding. This research provides a methodology for designing and evaluating curriculum around highly technical skills that are increasingly in demand in research, education, and industry careers.