For years, parents who wanted to keep their kids’ computer usage safe have heard the same advice.

Keep the family computer in a public place, share your child’s sign-ons and passwords and set rules about how long they spend in front of a screen.

These simple rules work great in Maine until your child hits 7th grade. Then the schools give them a laptop that goes anywhere, can be used anytime and under any on-screen identity the child chooses.

That’s why we support the Portland school district’s effort to put blocking screens on the laptops it issues, preventing student access to video games, online gambling and pornography sites, even when the student is at home.

If this sounds like a parent’s responsibility, it is. But the school system has not made doing that job easy.

With take-home laptops, schools have given teenagers unfettered access to the vast offerings of the Internet. Some experiences available to them are fantastically educational, but there are plenty of opportunities for missteps. Handing a laptop to a 12-year-old and hoping he sticks to the educational sites is like giving him a set of car keys and hoping he just goes to museums and national parks.

So far, most of the critics of the plan are those who are still looking forward to receiving a high school diploma. But some adults who should know better are bemoaning the limits, saying that exploring on the Internet is part of a student’s education and schools are intruding into what should be a family decision.

Neither complaint makes much sense, however. Schools, which are committed to education, have always blocked access to inappropriate sites on school grounds because those sites present more distractions than learning opportunity. By limiting a school-owned computer’s use, Portland is putting control back where it belongs, in the family.

If Portland parents want to buy a computer and give their child free and unlimited access to the Internet, they can do so. If they want to prohibit their student from most Internet access at home, they have that choice. And if they want to draw some age-appropriate limits between those poles, they will have a much easier time with the limits built into the school-issued laptops than they would without them.