This article reports a meta-analysis of 42 experiments in 33 published studies involving processing instruction (PI) and production-based instruction (PB) used in the PI studies. The comparative effectiveness of PI and PB showed that although PI was more effective than PB for developing receptive knowledge, PB was just as effective as PI for productive knowledge. Furthermore, the PB proved superior to the PI for productive knowledge when both groups received the same explicit information. The moderator analyses showed that: (i) the long term effects of PI and PB differed; (ii) PI was more effective for adults than for adolescent learners while PB was equally effective for both age groups; (iii) the effectiveness of PI was not influenced by the provision of explicit explanation and strategy training; (iv) the effectiveness of PB for receptive knowledge was influenced by strategy training; and (v) both PI and PB proved more effective in the production tests when the instruction focused on the meaning primacy principle than the first noun principle while no differences were found in the receptive tests.