A study in college-level English-as-a-Second-Language (ESL) instruction investigated (1) whether or not there is any relationship between the strategic use of explicit grammar knowledge, including metalinguistic concepts, in an attempt to recognize error, and the actual correction of error and success in academic ESL; (2) whether or not certain error types respond better to this treatment than others; and (3) how efficient this explicit knowledge is in terms not only of correction but also of time, an important consideration for students taking examinations. Subjects were 12 native Spanish-speaking ESL students in an English composition course. Each was asked to find a specific number of errors in passages and correct them, using a think-aloud protocol; all errors were genuine ones made by Spanish-speaking students. Results indicate that explicit knowledge was directly related to recognition and correction of error, and to success in required English courses. Explicit knowledge was most effective in treating morphological error. Although use of the explicit knowledge appeared relatively automatic, more successful students spent more time on explicated corrections than did less successful students, suggesting analysis is a crucial element of successful use of such knowledge. Theoretical and instructional implications are discussed. Contains 70 references. (MSE)