This article examines a variety of options for conducting investigations of the effects of interventionist form-focused instruction (FFI). Constructs related to three key areas of form-focussed instruction are presented; (1) the type of instruction, (2) the target of the instruction, and (3) the definition and measurement of "language acquisition". The constructs are illustrated by drawing on a representative set of FFI studies. The overall aim is to draw a conceptual map that can inform meta-analytical surveys of existing studies and the conceptualisation of new studies.