From the main results:
>In a cross-sectional model controlling for prior achievement, the (no cellphone) policy yields a 0.073 SD increase in GPA [b = 0.073, 95% confidence interval (CI) = (0.003, 0.144), one-sided P = 0.021].
I tried looking for the raw average GPA in each group to have more context on how consequential these reported standard deviation (SD) differences are, but can’t seem to find them in either the paper text or their supplementary materials. If someone has interest and better luck finding these, I’d appreciate it.