With the framework of the cognitive load theory, researchers have shown students in an experimental condition learned mathematics with worked-out examples significantly outperformed those learning mathematics in the control condition. The current consists of two experimental studies with 66 fifth grade students as participants. In Study 1, participants were divided into an experimental and a control condition, learning mathematics with the worked-out example instruction and traditional instruction, respectively. The result shows an aptitude-treatment interaction, that is, the worked-out example method was more beneficial for students for students with lower prior achievement, while the traditional method was more beneficial for students with higher prior achievement in mathematics. In Study 2, students were assigned to three conditions to learn mathematics, a condition with worked-out examples presented with PowerPoint, a condition with worked-out examples presented with hard copies, and a condition with traditional instruction. The results indicated that the students who received instruction with the worked-out example presented via PowerPoint gained significantly higher grades in a posttest of the mathematical achievement test than those who received the traditional instruction.