This study analyzes the mistakes with tenses that students of English make in a form-focused test (grammaticality judgment test) as opposed to a meaning-focused test (compositions). The data for the study narrowly analyses some verb tenses and verb forms. The results of the study demonstrate that after a year of English Grammar instruction at university advanced NNS students showed a significant difference between the rates found in both tests. The paper also offers some practical techniques to improve students? production of appropriate L2 written prose.