 Solution

The decisive experiment would be a sufficiently large Randomized controlled trial assigning children to meaningfully different durations or intensities of education, maintaining the assigned contrast, measuring refractive error before treatment and repeatedly afterward, and using blinded outcome assessment with complete follow-up. Randomization makes baseline causes of myopia exchangeable between arms in expectation, while assignment precedes the outcome; under adherence, no interference, and consistent measurement, the difference in outcome distributions estimates the causal effect of the assigned education policy. Such a trial would be ethically unacceptable because it deliberately withholds or imposes education, which explains the appeal of quasi-experimental and genetic approaches.