Primary research interests include the learning and teaching of the mathematics of measurement, geometric reasoning, the use of computer software to model mathematical ideas, and the professional development of teachers engaged in teaching elementary and middle-school level mathematics or science. Dr. Barrett is currently Principal Investigator of a four-year project, Learning Trajectories to Support the Growth of Measurement Knowledge: Pre-K through Middle School in collaboration with Douglas Clements and Julie Sarama at the University of Denver along with Craig Cullen, a colleague at Illinois State University. Barrett recently completed a related four-year project: A Longitudinal Examination of Children’s Developing Knowledge of Measurement: Mathematical and Scientific Concept and Strategy Growth from Pre-K to Grade 5 in collaboration with Douglas Clements and Julie Sarama at the University of Denver. Both projects are part of the Discovery Research K-12 Program of the National Science Foundation.