You have to admit that it's quite clever how they approximate phone use:

> Our identification strategy relies upon our ability to calculate school-specific measures of smartphone activity that we can attribute to students, rather than adults in the building. To do so, we use detailed smartphone activity data from Advan between January 2023 and December 2024 that we link to LUSD schools using point-of-interest coordinates.13 In particular, we focus on the average number of unique smartphone visits (pings) between 9am and 1pm on school days (a common time frame that elementary, middle, and high schools in LUSD are all in session during school days) in the last two months of the 2022-23 school year (right before the ban took effect) and the first two months of the 2023-24 and 2024-25 school years.14 To disentangle student activity from the smartphone activity of teachers/staff, we subtract the average number of unique smartphone visits between 9am and 1pm on teacher workdays (in the same school year) from the same average on regular school days.