The problems encountered by English as second language (ESL) students in selecting verb tenses for their written discourse were investigated. Tape recorded interviews with four freshman composition students who had been referred for intensive work on verb errors were analyzed for students' explanations of their errors and the contexts in which they appeared. The data revealed that ESL students had difficulty understanding how tense use was influenced by context and rhetorical or temporal stance. Second, the comprehensibility of tense choice was examined in the writing of native English speaking graduate students. Sixty native English speakers rated the texts in terms of clarity. Results showed a correlation between readers' judgments of clarity and writers' adherence to discourse level tense constraints described by Chafe (1972). These studies demonstrate that teachers should avoid contextless explanations or exercises on verb tense, and that the students' own writing provides the best basis for working on verb tense problems. Students should be taught how to manage the composing process and how good writers work. Guidelines for materials development are offered, and samples of the texts used in the second study and eight references are appended. (RW)