Understanding how atoms and molecules interact through intermolecular forces (IMFs) is necessary to progress on to more complex concepts in chemistry. For example, IMFs play an important role in how phenomena such as protein folding, DNA replication, or phase changes occur. Unfortunately, previous research has shown that IMFs are not well understood by students even after undergraduate-level instruction. To address this, the transformed chemistry curriculum CLUE (Chemistry, Life, the Universe and Everything) places a strong emphasis on understanding both how and why IMFs form and the role of IMFs in understanding chemical and physical properties. In order to better understand how students’ reason about IMFs and how we can further improve the CLUE curriculum, we used interview and homework data to develop a system to characterize the sophistication of students’ written and drawn explanations of London Dispersion Forces (LDFs), the most basic type of IMF. We then used this characterization system to analyze the responses of two matched cohorts of students throughout the ﬁrst two semesters of general chemistry. This analysis allows insight into how the CLUE curriculum impacts students’ understanding of LDFs throughout the two semester sequence while also informing future modifications to the curriculum to improve the instruction of LDFs. This design based process of using student output to iteratively reﬁne a course provides an example of how course improvement can occur.