= 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.
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