My son, Joe, and his wife have three sons, ages 10, 8 and 5. Like many parents, they are trying to limit the time the boys spend staring at computer screens. Their California school system and the state are making that difficult.

Joe noticed that the World Health Organization warned of too much screen time. The state recommended no more than 60 minutes after school. Yet his sons’ school required schoolwork and homework on computers after second grade. And the annual state tests were online.

He felt he and his wife had a simple message — stay away from screens. Now, they were contradicting themselves — first, get on the computer, and do your homework, then, get off the computer, and avoid too much screen time. His sons found it easy to switch from homework to online games, some of which they discovered on their school district’s website.

Now comes another headache for parents like him. A report on computer use and school achievement found that “when students report having access to classroom computers and using these devices on an infrequent basis, they show better performance. But when students report using these devices every day and for several hours during the school day, performance lowers dramatically.”

The report was done by the Paris-based nonprofit Reboot Foundation working with education experts who studied student achievement using statistical methods. The foundation was founded and funded by Helen Lee Bouygues and her family to research critical thinking in education. Bouygues, who wrote the report, is a veteran business executive.

The report said that in key areas, the trend of achievement declining when screen time expands “holds irrespective of the student’s background, such as their income status or identification as having a disability.” Bouygues said she is reporting only “associations between school computer use and performance” and “cannot make cause and effect inferences.”

The study used achievement results and answers to questions about screen time from the 2015 Program for International Student Assessment (PISA) test of 15-year-olds and the 2017 National Assessment of Educational Progress (NAEP) tests of several age groups in U.S. schools.

Teacher complaints about the way they are trained to use technology may be right. The report said the NAEP results, particularly in math, showed the trend toward lower student performance “also holds regardless of the teacher’s background and preparation in technology-based instruction.”

This report has not gone through formal peer review, but the methods were reviewed by experts at the Albert Shanker Institute and the Organization for Economic Co-operation and Development, which does the PISA tests.

Bouygues said technology could elevate critical thinking. “Educational software can be an ideal environment for students to practice these higher-order reasoning skills, and some companies have already developed products to inspire this practice in the classroom,” she said.

But how does anyone identify such programs in the flood of material jamming school district inboxes? “Some of the software that is currently branded as ‘educational’ has limited educational value,” the report said. “One recent study of 49 middle schools found that over a third of technology purchases made by the schools were never utilized.”

Bouygues suggested parents sort out the promotional junk by asking good questions. What kind of learning does this technology support? How much time should our children spend on it?

In my experience, parents rarely do that. They tend to believe computer technology is necessary in this century. They are pleased to see it but don’t have time to look closely. Many administrators find inquisitive parents an annoyance. Administrators may praise the material they have bought without going into detail.

Questions about expansion of screen time get similar responses. In writing about his experience for other publications, Joe said that when he complained about this to teachers, parents and even state officials, most told him it was his job as a parent to police screen time — just like his parents policed his TV time.

I have two thoughts: (1) I don’t remember my wife and I policing Joe’s TV time when he was a child. (2) I suspect many parents of our generation were equally inattentive.

Joe noted a crucial difference between then and now: He wasn’t required to do his homework on TV.