Data literacy is recognized as a critically important skill in today's society, but thinking with and about data is often ignored in K-12 curricula. The Thinking With Data (TWD) project advocates that data literacy is a skill that should be addressed in an interdisciplinary manner. This article provides an overview of the TWD curriculum for middle school, which uses an extended Preparation for Future Learning (PFL) framework to teach data literacy across subjects. Research conducted during field implementation of the curriculum in two middle schools investigated whether the approach worked, and if so, why. Results show evidence of student gains in data literacy skills as well as in mathematics and science. Our best evidence of learning of data literacy skills was found during the social studies and mathematics modules. While we have preliminary evidence of learning in science and language arts, potential gains in these modules need to be more closely examined. (Contains 5 tables and 4 figures.)