After-school settings provide youth with homework support, social outlets and fun activities, and help build self-confidence. They are safe places for forming relationships with caring adults. More after-school settings are starting to integrate Science, Technology, Engineering, and Mathematics (STEM) topics. What science skills and concepts might youth learn in engineering design-based after-school settings? Traditional assessments often fail to capture the ways youth learn in informal settings, and deep science understandings are notoriously difficult to measure. In this study, we examined three after-school settings where 65 youth were learning science through engineering design challenges. In this informal setting, we examined storyboards, social networking forum (SNF) chat logs, videos of whole-class interactions, interviews with groups and single participants, and traditional multiple-choice pre- and posttest results. As we looked for evidence of learning, we found that the social networking forum was rich with data. Interviews were even more informative, much more so than traditional pencil and paper multiple-choice tests. We found that different kinds of elicitation strategies adopted by site leaders and facilitators played an important role in the ways youth constructed knowledge. These elicitation strategies also helped us find evidence of learning. Based on findings, future iterations of the curricula will involve tighter integration of social networking forums, continued use of videotaped interviews for data collection, an increased focus on training site leaders and facilitators in elicitation strategies, and more open-ended pencil and paper assessments in order to facilitate the process of looking for learning. (author abstract)