This study investigates whether lesson plans created by ChatGPT improve students' math achievement in primary school. A pretest-posttest control group experimental design was used with 39 third-grade students (24 in the experimental group, 15 in the control group). The experimental group followed lesson plans created using ChatGPT, while the control group used existing lesson plans. The study found that students' math achievement significantly increased (d = 1.268) when lessons were based on ChatGPT lesson plans. However, the difference between the posttest scores of the experimental and control groups was not statistically significant. These results suggest that ChatGPT lesson plans are effective in improving academic achievement. Teachers should consider ChatGPT and their own plans, combining them to benefit from both. The study highlights the potential of ChatGPT in education, but also notes the need for careful use to avoid issues such as bias, ethical violations, and misinformation. While ChatGPT lesson plans showed a very large effect on math achievement, the study found no significant difference between the two groups in posttest scores. This indicates that both ChatGPT and traditional lesson plans are effective in improving math achievement. The study emphasizes the importance of integrating ChatGPT into education while ensuring its responsible use.This study investigates whether lesson plans created by ChatGPT improve students' math achievement in primary school. A pretest-posttest control group experimental design was used with 39 third-grade students (24 in the experimental group, 15 in the control group). The experimental group followed lesson plans created using ChatGPT, while the control group used existing lesson plans. The study found that students' math achievement significantly increased (d = 1.268) when lessons were based on ChatGPT lesson plans. However, the difference between the posttest scores of the experimental and control groups was not statistically significant. These results suggest that ChatGPT lesson plans are effective in improving academic achievement. Teachers should consider ChatGPT and their own plans, combining them to benefit from both. The study highlights the potential of ChatGPT in education, but also notes the need for careful use to avoid issues such as bias, ethical violations, and misinformation. While ChatGPT lesson plans showed a very large effect on math achievement, the study found no significant difference between the two groups in posttest scores. This indicates that both ChatGPT and traditional lesson plans are effective in improving math achievement. The study emphasizes the importance of integrating ChatGPT into education while ensuring its responsible use.