This paper reports on a study that attempts to investigate the acquisition orders of the English interrogatives established in three groups of Cantonese classroom learners. A goal of the study is to examine the effect of formal instruction on second language acquisition, to discover whether different intensity of classroom instruction has an effect on the acquisition order. Within the framework of the study, an attempt was made to separate interlanguage (IL) knowledge from production, with an underlying assumption that classroom learners might know more than they could produce. It is revealed that IL development of the three groups of classroom learners largely conformed to the universal sequence of development as far as production is concerned. Moreover, difference that may be attributable to IL variability between knowledge and production were also found. Rules relating to Subject-Verb inversion established from the learner's IL knowledge did not coincide with those established from production. (Author/JL)