Reviews of the SLA literature on the effects of instruction show that instruction can have positive effects on acquiring an L2 but that those effects are generally moderated by variables, of which instruction type is an interesting example in instructional settings. This study, involving 216 intermediate ESL learners, investigated the effects of two types of practice-based instruction on the acquisition of tense (past vs present perfect) in L2 English. Three computer-administered pretest–treatment–posttest experiments were designed, in which we experimentally manipulated Time (pretest, posttests) and Treatment (input practice vs. output practice, along with input only in Experiment 1 and no-treatment control in Experiment 3). Both input practice and output practice, preceded by explicit rule presentation, produced significant effects, equally large in two receptive test tasks (grammaticality judgment and selective response) and in two productive test tasks (constrained constructed response and translation). Although this study failed to obtain differential effects of input practice and output practice, it did obtain strong effects for both forms of practice on performance in both receptive and productive tasks, in contrast to a no-treatment control condition.