This article proposes an approach to explicit grammar instruction that seeks to develop metalinguistic knowledge of the L2 and raise L2 learners' awareness of their L1, which is crucial for the success of second language acquisition (Ellis 1997, 2002). If explicit instruction is more effective than implicit instruction (Norris and Ortega 2000), the question is what is to be taught explicitly. Research in theoretical linguistics enables us to define what specific metalinguistic knowledge underlies certain lexical items and grammar constructions. The present study illustrates this by using simple sentential constructions that are regarded as A2 grammatical features according to Hawkins and Filipovic (2012). B1-level Japanese learners of English tend to omit objects (Objs) of different types, when producing simple A2-level sentences. We attribute this problem to two linguistic factors. First, verbal argument structure that defines what elements, e.g., subject (Sbj), Obj and other obligatory sentential elements, are required to appear with a given verb. Second, English and Japanese differ with respect to the omission of required element(s). This study claims that metalinguistic knowledge of argument structure and overt versus covert realization of arguments in the two languages should be explicitly taught through structure-based tasks. We propose two different sets of such tasks: (i) instruction that focuses on lexical properties by presenting verbal argument structure and then requiring students to engage in grammaticality judgment and controlled written production tasks; (ii) instruction that focuses on language-particular features by giving students consciousness-raising tasks in L1, consciousness-raising tasks that compare and contrast L1 and L2, controlled-writing tasks, and free-writing tasks with corrective feedback.