This study investigated the effects of input and output on the development of L2 knowledge. Participants included 129 third-semester Persian learners of English enrolled in 5 intact EFL classrooms functioning as four experimental groups and one control group. Two experimental groups received two types of input-based instruction, which differed from each other in terms of the saliency and the number of tokens of target structures in the input. Participants in another experimental group received instruction that required them to produce meaningful output that contained target structures. The last experimental group that only received explicit instruction about target structures was included in the study to specify the moderator role of explicit instruction, which was also included in the input-based and output-based instruction. The results of grammaticality judgment, multiple choice grammar, and written production tests administered as pre-test, immediate and delayed post-tests suggested that both input-based and output-based instruction can lead to the development of L2 knowledge. Our findings also support the claim that more obtrusive input in which target structures are more salient to learners has more positive effects on L2 development than just exposing learners to more tokens of target structure. (Contains 7 tables and 3 figures.)