This study compares Spanish instructors' use of preterite and imperfect in the foreign language classroom to the distribution of these forms in large-scale corpora, which represent the input learners would potentially receive in a naturalistic learning context. Twenty-four 50-minute class sessions were recorded, and all tokens of preterite and imperfect spoken by the instructors were transcribed. Each token was coded for the verb, its morphological ending, the instructor's native language, the class activity during the token's utterance, and the class level. For all verbs that were analyzed in the instructor input, their preterite and imperfect token frequencies in the oral data of two Spanish corpora were determined. Results revealed low token and type frequencies for imperfect morphology in instructor input. The imperfect accounted for only 18% of past tense forms, with class activity as a significant predictor of its use. In contrast, around 60% of past tense tokens of these same verbs in large-scale corpora were imperfect, and fewer verbs were biased toward use in the preterite. In sum, the distribution of past tense forms in instructor input differed substantially from that of the corpora.