This document summarizes the development of a diagnostic test to evaluate students' data analysis skills. The authors developed a 23-question multiple choice test covering key skills like precision, accuracy, error analysis and graph interpretation. They administered the test to over 1200 students across 10 institutions, finding that skills development is not consistent and later-year students did not necessarily perform better. They propose augmenting the test with online learning resources to help address misconceptions and make data analysis skills development more explicit in curricula.