This study examined the effectiveness of two instructional mind-mapping approaches to stimulate fifth and sixth graders' graphical summarization skills. Thirty-five fifth- and sixth-grade teachers and 644 students from 17 different elementary schools participated. A randomized quasi-experimental repeated-measures design was set up with two experimental conditions and one control condition. Students in the experimental conditions followed a 10-week teacher-delivered instructional treatment working with either researcher-provided or student-generated mind maps. Multilevel piecewise growth analysis was used to examine differences between classes and between students within classes, as well as the growth in students' graphical summarization skills and its relationship with class-level (i.e., instructional approach) and student-level (i.e., gender, grade, home language, and achievement level) characteristics. Results show the greatest overall gains for students in the student-generated mind-map condition as to the quality of their informative text traces and graphical design. However, no significant differences between the experimental conditions were found as to the quality of the graphical content. Only for gender and grade were significant interaction effects with the instructional approach found.