Researchers have hypothesized strong connections between Computational Thinking (CT) practices and STEM learning. However, there is a lack of consensus on what constitutes an adequate set of CT knowledge and skills. In this paper, we present an initial framework for evaluating students’ CT learning. We introduce the primary CT concepts and practices that students can learn and apply in a learning by modeling environment. Our overall goal is to develop assessments that study the synergy between STEM and CT concepts in K-12 curricula. Towards this end, we discuss the results from a teacher-led classroom study we conducted on STEM- and CT-learning in our CTSiM environment.