This paper describes the development and validation of the Cognate Awareness Test (CAT), which measures cognate awareness in Spanish-speaking English Language Learners (ELLs) in fourth and fifth grade. An investigation of differential performance on the two subtests of the CAT (cognates and noncognates) provides evidence that the instrument is sensitive to English-Spanish cognate awareness among elementary school-age Spanish-speaking ELLs. Cognates were highly correlated with the children's Spanish WLPB-R Picture Vocabulary scores, whereas noncognates were highly correlated to children's English WLPB-R Picture Vocabulary scores. (Contains 4 figures and 9 tables.)