In the 90s, SLA research began to present empirical evidence that form-focused-instruction (FFI) has long-lasting positive impacts on the acquisition of specific syntactic features, which are acquired in predictable sequences of interlanguage development as proposed by Pienemann's (1986) Multidimensional Model. For example, three published studies reported the sustained effects of FFI on the acquisition of interrogatives in normal ESL classes with school-age children (Spada & Lightbown, 1993) and in experimental classes with adult ESL learners (Mackey, 1999; Mackey & Philp1998). These supported Pienemann's (1984) Teachability Hypothesis, which claims that learners can benefit from FFI if it targets the next stage of their L2 development rather than a stage further beyond the learner's current level. These findings have provided a better understanding of both the acquisition of developmental question formation and the effective instructional means to promote its acquisition. However, few studies have investigated these issues in the EFL context, let alone, in intact EFL classrooms. Moreover, the previous FFI research has not explored the acquisition of interrogatives at higher stages (5 and 6) and little is understood about what types of intervention are effective in promoting adult learners' acquisition of interrogatives. My research aims to investigate the issues raised above and also to examine the effect of collaborative dialogue in learner-learner interaction, which is thought to play a beneficial role in promoting noticing necessary for interlanguage development (Swain & Lapkin, 1998).