Formulating questions is one crucial building block of communication. Regarding wh- questions, though, literature often reports that Japanese EFL learners tend to have greater difficulty correctly formulating subject questions than other types of questions. This study attempts to shed more light on this phenomenon. In Study 1, university students tried writing 50 wh-questions asking for certain pieces of information specified by underlines in source statements. The results led to a hypothesis that subject questions are a challenge only when the wh-word is immediately followed by a lexical verb but they are not particularly difficult when the wh-word is followed by a primary or model verb. Study 2 tested that hypothesis on two separate groups of university students. It also investigated the effect of explicit grammar teaching by conducting practice sessions with one group (experimental group) and not giving such sessions with the other (control group). The results confirmed that the difficulty of making subject questions is indeed moderated by the type of verb that follows the wh-word and indicated that explicit and focused practice of formal manipulation can help learners overcome the revealed weakness.