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Causal efficacy is best supported by rigorous comparative evidence that isolates the intervention. Option B provides a randomized controlled trial (RCT) with a concrete effect size on a common outcome measure (the same standardized test), establishing that the program caused higher scores relative to a valid counterfactual. Option A is anecdotal and subject to positivity bias; it does not measure learning. Option C indicates usage, not impact—attendance can be high without achievement gains. Option D is suggestive but confounded: districts differ in many ways, so cross-district comparisons aren’t causal. GRE Argument strengthening tasks reward (1) random assignment (to neutralize confounds), (2) objective outcome metrics aligned with the claim, and (3) a clear time frame. Option B satisfies all three, making it the strongest support for the board’s assertion.