In a statement, the district says it could be construed as a political statement and could be a disruption in the classroom.
The safety pin has emerged as a statement following the election of Donald Trump as the country's 45th president.
The pin is a symbol of solidarity with minorities, refugees and immigrants.
On Monday night, parents, students and others "packed" a school board meeting to protest, David Twiddy of the Kansas City Star says. When school Superintendent Jim Hinson compared the ban on safety pins to the current ban on the confederate flag, the crowd became "incensed," Twiddy said.=
The state National Education Association is supporting the teachers.
"The disruption starts when the kid walks through your classroom door afraid. It is happening, and teachers have to deal with that," said NEA spokesman Marcus Baltzell.
CNN contributed to this report.