This study devised an approach utilizing advertisements for cognitive education, particularly training to foster critical thinking ability of elementary students and conducted a field experiment to verify its educational effect. Fourteen sessions of the critical thinking education were performed over one semester geared toward elementary students in the fifth and sixth grades. Results indicated that students who received critical thinking education using advertisements made statistically significant improvements in both critical thinking skills and critical thinking dispositions, compared to students who did not receive this education. These results demonstrate that education using advertisements as learning materials can help elementary students to improve their critical thinking ability. We discussed several implications of our results for educational practice as well as directions for follow-up studies.