There is a strong case to be made that the goal of science is to develop explanatory theories that help us organize our understanding and make predictions about the natural world. What then, is the goal of science education? What is it that we want students to know and be able to do, and how do we achieve these goals? Here, I argue that one overarching goal is to help students construct causal, mechanistic explanations of phenomena. In chemistry this means we are working to help students use their understanding of molecular level interactions to explain and predict macroscopic events. Furthermore, while constructing explanations is an important goal in itself, the very act of constructing explanations helps students develop a deeper understanding, and provides the kind of intellectual satisfaction that memorizing facts cannot. I hope to convince you that our current approaches to assessing student learning are, in fact, all too often counterproductive and almost certainly contribute to students' inability to connect ideas and develop a useful understanding of chemistry and that these assessments send the wrong message about what chemistry means (and why it is valuable). I will offer some suggestions how we might design more meaningful approaches to curriculum development and assessment of student understanding. After reading this essay, I hope that I will have convinced you that: (i) if we value something, we must assess it; (ii) we cannot assume students will construct a coherent framework from the fragments we teach; and (iii) we must design assessments that provide us with enough evidence to make an argument that the student understands.