Students need to learn how to engage in several scientific practices in order to be considered proficient in science. Many of these practices are needed to evaluate scientific claims made in the popular media. Yet, there are few instruments available that science educators can use to assess whether students can apply what they know about scientific practices in order to critique scientific media reports. In response to the need for valid, reliable, and informative assessments of knowledge of scientific practices that are not embedded in complex scientific content, an instrument was developed and validated over two iterations. This assessment satisfied construct, content, face, concurrent, and discriminant validity checks for different undergraduate student populations, and the item analysis demonstrated that each item was informative for this subset of the general population. This instrument will allow instructors to compare student performance across space and time, promoting and supporting research on the teaching and learning of scientific practices.