This paper examines whether participation in extra classes improves children's cognitive test scores, using data from the second and third rounds of the Young Lives survey in Vietnam. Using a standard value-added model, we find that that the number of hours pupils spend in extra classes is not associated with better cognitive (mathematics and vocabulary) test scores. However, a number of other factors (parental schooling, household wealth, ethnicity and gender) do influence children's test scores. These results are robust to different estimation methods and model specifications. The findings suggest that the large amounts that the parents of Young Lives children spend on extra classes cannot be justified from a cognitive standpoint.