Along with cell phones, the mayor may as well ban pencils, pens, and paper if he is trying to rid schools of things children use to make mischief, the teachers union president, Randi Weingarten, said in a legal brief submitted last week.

The brief was filed in support of a group of parents suing the city to end a cell phone ban in the public schools. Mayor Bloomberg has said the intention of the ban is to help teachers manage their classrooms and avoid disruptions. Ms. Weingarten says teachers and schools don’t need the help.

“We’ve always agreed that cell phones are very disruptive in classrooms and schools and should not be used, period,” she said, but added: “Parents are very mobile and kids are very mobile, and they are perceived as a very important communication connection between parent and child.”

In the past, Ms. Weingarten has appeared at parent protests and vocally opposed the ban. In the brief, she supports the plaintiffs’ argument that children need cell phones traveling to and from school for safety reasons. As for children that use phones for cheating, taking illicit pictures, and other such mischief, she says schools and teachers should be left to deal with troublemakers.

Rather than a blanket citywide ban, “empowering educators and parents to develop a school-by-school cell phone policy is more appropriate, ” she wrote in the brief, suggesting that having students turn off phones or store them in lockers may work in many cases.

The plaintiffs may not be pleased by all of Ms. Weingarten’s conclusions in the brief. She says some schools might be justified in banning cell phone possession altogether for the handful of students that “violate such a policy as they do the existing cell phone ban.”