A meta-analysis was conducted to investigate the effects of explicit and implicit instruction on the acquisition of simple and complex grammatical features in English. The target features in the 41 studies contributing to the meta-analysis were categorized as simple or complex based on the number of criteria applied to arrive at the correct target form (Hulstijn & de Graaff, 1994). The instructional treatments were classified as explicit or implicit following Norris and Ortega (2000). The results indicate larger effect sizes for explicit over implicit instruction for simple and complex features. The findings also suggest that explicit instruction positively contributes to learners’ controlled knowledge and spontaneous use of complex and simple forms.