Covariational reasoning (or the coordination of two dynamically changing quantities) is central to secondary STEM subjects, but research has yet to fully explore its applicability to elementary and middle-grade levels within various STEM fields. To address this need, we selected a globally referenced STEM assessment--the Trends in International Mathematics and Science Study (TIMSS)--to investigate the extent to which covariational reasoning could be applied. Specifically, we identified the frequency of items with potential to elicit students' covariational reasoning through a content analysis of publicly released TIMSS 2011 items in Grades 4 and 8 mathematics and science. We found that approximately one-third of items in all grades and subjects had potential for covariational reasoning, and many of these items had such potential with no viable alternative strategy. Furthermore, items in every content strand and cognitive domain had potential for covariational reasoning. We interpret these findings as indicative of the salience of covariational reasoning across STEM education, and we discuss the implications of these results for research, assessment, and instruction.