What do cows drink? The correct answer is water, but many are tempted to say milk. The disposition to override an intuitive response (milk) with a more analytic response (water) is known as "cognitive reflection." Tests of cognitive reflection predict a wide range of skills and abilities in adults. In this article, we discuss the construction of a developmental version of the cognitive reflection test and explore how it predicts rational thinking and normative thinking dispositions in elementary school-aged children, independent of age, executive function, and cultural context. We also explore how the test predicts children's mastery of counterintuitive concepts in science and mathematics. Findings suggest that cognitive reflection may be a prerequisite for developing, and improving, analytic thought, thus highlighting the value of studying cognitive reflection from a developmental perspective.