This study investigates differential effects of form-focused instruction (FFI) on the development of explicit knowledge versus implicit knowledge of a second language (L2) when the FFI is offered within the context of meaning-focused instruction (MFI). Forty-two adult learners of English participated in the study and were randomly assigned to a group who received FFI before MFI (FM), a group who received FFI after MFI (MF), a group who received MFI only (M), or a control group. Learning was measured by an untimed grammaticality judgment task (UGJT), a primary measure for explicit knowledge, and an elicited oral imitation task (EOIT), a primary measure for implicit knowledge. The results illustrate that, despite both FM and MF groups’ improved performance on the UGJT, only the FM group showed a positive developmental trend on the EOIT. No clear learning effect was observed among the M group learners or the controls. Therefore, the findings suggest that FFI prior to MFI supports the development of implicit knowledge more efficiently than FFI delayed until after MFI has begun.