Another dodgy Lancet study

Jon Haidt and others write:

A recent study published in The Lancet (Goodyear et al., 2025) has generated newsheadlines suggesting that restricting phone use in schools has no effect on the wellbeing or academic performance of students. This contradicts several previousstudies that did find such benefits.

Haidt notes:

In reality, the study was primarily a comparison of schools with a classroom ban versus schools that let students keep their phones with them at all times, in their backpacks.

Basically it was not comparing schools with no restrictions against schools with a total ban. It was just comparing schools around the middle.

The data in this study was correlational—they did not conduct a study designed to estimate a causal effect. For instance, they might have collected data before and after schools implemented phone policies (as was done here in a study that did find improvements in academic performance)

The latter would be valuable – before and after difference within a school.

Haidt suggests what would be a good study:

Ideally a group of schools could be identified in which some schools will change their policies at the start of the next school year, while other schools maintain a permissive policy. That would provide a control or comparison group (although not one selected by random assignment), which would allow a “difference in difference” study that compares the changes in the schools that changed policies to the changes in schools that did not change policies.”

So basically the Lancet study doesn’t tell us much at all.