This study investigates the development of two levels of morphological knowledge that contribute to Spanish-English bilingual students' ability to recognize cognates: the ability to recognize a cognate stem within a suffixed English word, and knowledge of systematic relationships between Spanish and English suffixes (e.g., the fact that English words ending in "-ty" often have a Spanish cognate ending in "-dad". A total of 196 Latino bilingual students in fourth, sixth, and eighth grades, were asked to give the Spanish equivalent for English words, some of which had derivational and inflectional suffixes. Results indicate that students' ability to translate cognates increases with age above and beyond any increase in their vocabulary knowledge in Spanish and English. There was also marked growth in students' knowledge of systematic relationships between Spanish and English suffixes. Students recognized cognate stems of suffixed words more easily than non-cognate stems, suggesting that in closely-related languages such as Spanish and English, cross-language transfer may play a role not just in recognizing individual words but also in the learning of derivational morphology. (Author)