Problem-based learning (PBL) simulations for middle school students, designed to promote a 21st century science, technology, engineering and math (STEM) skills. Using a web-based communications system and a PBL simulation in a research environment, GlobalEd 2 links classrooms of students who are separated by physical distance and socioeconomic boundaries, with one another in an engaging and active game context as they play the role of international science advisors. This paper presents findings from a set of simulations (student n=535). Results indicate positive changes in students' knowledge about science content related to two different simulations - Water Resources and Climate Change. The implications of these results are discussed along with directions for future research. [ABSTRACT FROM AUTHOR]