I'm usually glad that Mayor Bill de Blasio is a public school parent like me. Unlike his predecessor, he more readily understands our frustrations with large class sizes and standardized testing.

But parents sometimes can miss the larger picture. By lifting the cellphone ban in schools, the mayor shows that he's thinking like a dad. Good for him, but schools exist to educate kids, not to necessarily make parents happy.

I understand why the Middle Class Helicopter Parent-in-Chief wants to be able to reach his son during the day, and might want to know where he's going after school. But educators have excellent reasons to want phones out of the classroom.

I teach at Brooklyn College, where electronic distraction is annoying, but at least the students are old enough to really understand they risk failing my class -- and, I like to think, missing out on a great discussion -- if they're zoned out on Instagram or hotchatting boyfriends.

If my 9-year-old son and his friends had cellphones, their teachers would have a far more serious problem. The kids would play Candy Crush, take selfies and watch "Epic Rap Battles of History" on YouTube all day. The Department of Education's new rules recommend that the phones be stored out of sight, but I'm not sure policymakers really understand the addictive nature of smartphones -- particularly for children.

Kids already spend too much time on screens at home: more than seven hours a day on average, for children ages 8 to 18, according to the Campaign for a Commercial-Free Childhood, an advocacy group. For low-income African-American and Latino kids -- most of our public school students -- the rates are higher, the group has found. Excessive screen time has been linked to social and emotional problems, hyperactivity and, surprise, poor school performance.

Parents feel safer when their children carry cellphones. But kids traveled to school before the invention of cellphones and when the New York City crime rate was much higher. NYC kids are now safer, but because technology exists to track them, parents can't resist.

Dad de Blasio understandably wants to know what Dante is up to. But Mayor de Blasio should reconsider lifting the ban.

Liza Featherstone lives and writes in Clinton Hill.