This paper examines possible improvement to problem solving skills as a function of playing the video game "Portal 2." Stealth assessment is used in the game to evaluate students' problem solving abilities--specifically basic and flexible rule application. The stealth assessment measures will be validated against commonly accepted external measures. For instance, basic rule application will be correlated with Raven's Progressive Matrices, and flexible rule application will be correlated with the Uses test, insight problems, and the compound remote association test. Improved problem solving outcomes will support our claim that "Portal 2" can be an effective method to enhance problem solving skills--one of the most important cognitive skills in the 21st century. [For the full proceedings, see ED562107.]