In this study, we have synthesized the research on visualization and representation to propose a model consisting of 4 major components of visualization competence in learning science: constructing, interpreting, transforming, and critiquing visualizations. We have developed and validated an assessment that measures students' visualization competence of matter (VCM). We administered the VCM assessment to 762 7th to 12th grade students at 2 public high schools in Taiwan. The students had started to learn concepts of matter at the particulate level in the 7th grade. However, traditional assessments rarely measure students' visualization competence in science. It was therefore unclear how well the students performed on visualization of matter across grade levels. Overall, the results indicated that the students' visualization competence of matter improved as they advanced to higher grades. A significant factor accounting for the development of their visualization competence of matter is their course experience, not their age or gender. We also found that content knowledge plays only a conditional role in students developing visualization competence of that content. Implications and future studies are discussed.