This study employed (and reports in detail) systematic procedures for research synthesis and meta‐analysis to summarize findings from experimental and quasi‐experimental investigations into the effectiveness of L2 instruction published between 1980 and 1998. Comparisons of average effect sizes from 49 unique sample studies reporting sufficient data indicated that focused L2 instruction results in large target‐oriented gains, that explicit types of instruction are more effective than implicit types, and that Focus on Form and Focus on Forms interventions result in equivalent and large effects. Further findings suggest that the effectiveness of L2 instruction is durable and that the type of outcome measures used in individual studies likely affects the magnitude of observed instructional effectiveness. Generalizability of findings is limited because the L2 type‐of‐instruction domain has yet to engage in rigorous empirical operationalization and replication of its central research constructs. Changes in research practices are recommended to enhance the future accumulation of knowledge about the effectiveness of L2 instruction.
Norris et al. (2000) studied this question.