This is a work-in-progress. The dramatic decline in youth interest in science, technology, engineering and mathematics (STEM) during adolescence has been a phenomenon of societal concern for several decades. Researchers have documented the decline in youth math and science interest during and after middle school, noting an even greater decline amongst females and minorities. Results of structural equation modeling (SEM) from a previous study indicate girls' interest in life sciences, a non-analytical area, differs from boys' interest and that out-of-school STEM experiences may have a positive impact on student interest in STEM. Both of these findings have implications for how to predict STEM interest and design instruction for more students, especially since the study of physics, an analytical course, is less attended by girls and considered the gateway to engineering. This research utilizes surveys, observations, interviews and focus groups in an all-girls after-school STEM program, and expands upon the constructs of science, math, and STEM interest to consider additional affective components such as empathy and belonging that may play a key role in improving girls' interest in STEM, especially engineering.