Although diagram use is considered to be one of the most effective strategies for solving problems, reports from applied educational research have noted that students lack spontaneity in using diagrams even when teachers extensively employ diagrams in instructions. To address this problem, the present study investigated the effectiveness of teacher-provided verbal encouragement (VE) and practice in drawing diagrams (PD), as additions to typical math classes, for promoting students' spontaneous use of diagrams when attempting to solve problems. The participants were 86 8th graders who were assigned to one of four instruction conditions: VE+PD, VE only, PD only, and with no addition to typical instruction (Control). The highest improvement in spontaneous diagram use was observed in the VE+PD condition. This finding suggests that, to promote spontaneity in students' diagram use, helping students appreciate the value of diagram use is important, as well as developing procedural knowledge in using diagrams.