Studies have shown that inferential questions encourage a more in-depth understanding of texts and that students need to learn appropriate strategies for answering them, particularly when they deal with multiple texts. In this experimental study, the authors aimed to improve eighth-grade students' (13- to 14-years old) ability to answer intra- and intertextual inferential questions when they read one or multiple complementary texts. The intervention was implemented by a group of middle-school history teachers. Teachers in both the intervention and control groups (IG and CG, respectively) taught the same teaching unit using the same reading materials. However, teachers in the IG participated in 12 hours of professional development seminars on analysis of their classroom practice and how to improve their questioning strategies. Post-intervention results revealed that students in the IG were significantly better than those in the CG at answering intra- and intertextual inferential questions. This difference was maintained at follow-up (2 months after finishing the intervention). Students in the IG also performed better than those in the CG at a learning test. These results confirm the value of teaching students how to answer complex questions, especially when they refer to more than one text. The findings also support the value of the professional development program that enables teachers to reflect on their practice.