This study investigated factors promoting the use of self-constructed diagrams by examining students' perceptions and daily class activities, and comparing Japanese (n = 291) and New Zealand (n = 323) students. Algebra word problems and a questionnaire were administered. The results revealed that the New Zealand students used diagrams more often and scored higher than their Japanese counterparts. Lack of confidence and perceptions of difficulty in diagram use, and viewing diagrams more as a strategy that teachers use, were found to link with lower use. Possible ways of promoting diagram use in math word problem solving are discussed.