The purpose of this study is to explore the effects of diagram-reading instruction on seventh graders’ reading performance. The researchers adopted the pretest-posttest nonequivalent groups of quasi-experimental design. 32 seventh graders, two classes, in Hualien participated in this study. The treatment group (n =16) received diagram-reading instruction-approximately 2 times each week, over a 9-week period, 810 minutes, while the control group (n = 16) was taught by regular Chinese instruction. We used PISA-style and divergent diagrams on daily life as the teaching materials. Several tools, such as “motivations for reading questionnaire”, “diagram comprehension test”, “videotapes and audiotapes in the classroom”, “course satisfaction survey”, “course feedback questionnaire’, “course interview questions”, and “instructor’s reflection notes” were used to collect quantitative and qualitative data. Results indicated no statistically significant differences between treatment group and control group on reading motivation and diagram comprehension. However, qualitative data showed diagram-reading instruction was distinctive and practical so that it could promote students’ learning interest. In addition, diagram-reading instruction could enhance students’ ability to read the diagram systematically. Therefore, diagram-reading instruction still revealed students’ positive reading motivation and diagram comprehension. Possible explanations for no significant quantitative effects in results, as well as implications for practice and research are discussed.