This study developed a web-based multimedia whiteboard system to help students learning with mathematical problem solving. The purpose is to promote a new online mathematical learning model that students not only use electronic whiteboard to write down their mathematical problem solving solutions but also use voice recording tool to give oral explanations about their thinking behind the solutions. To cultivate students' critical thinking capability and encourage collaborative peer learning, the new learning model also requests students to criticize others' solutions and reply to others' arguments. With the multimedia supporting tools, students can communicate easily with each other about what they think and how they solve mathematical problems. We have conducted an experiment with sixth grade primary school students for evaluation. After the experiment, a questionnaire about students' attitude toward the multimedia whiteboard system for math learning was then held. The results show that students were satisfied with the use of the multimedia whiteboard system for helping them with learning fractional division. Most students were interested in studying mathematics with the multimedia whiteboard system and thought this tool is particularly useful for doing collaborative learning. After analyzing the recorded solving processes and discussions content of students, we found that the performance of female students was superior to male students in communications and mathematical problem solving. Additionally, students with higher final exam grades had better mathematical abilities for doing critiques, arguments and communications.