The board adopted the policy in a 6-4 vote. Up to now, most Kansas districts had an "opt-out" policy, they enrolled children in sex ed unless a parent objected in writing.
Only a few other states have such "opt-in" requirements on sex education, according to the Sexuality Information and Education Council of the United States, a group that promotes sex education. Among them: Arizona, Nevada and Utah.
Board members who voted for the new policy said some parents told them they did not know their children were taking sex education until the classes had started.
"It's about empowering parents. That's the bottom line," said board chairman Steve Abrams.
Critics of the measure said that the children whose parents who won't see a permission form or won't turn it in are the ones most likely to need the courses. Some also said that the rule may violate the Kansas Constitution, which gives local school boards broad authority.
One board member wants the new policy to go further and require abstinence-only courses. "We need to send the correct message," Kathy Martin said.
Under her proposal, a school could lose its state accreditation if it did not offer nine weeks of instruction on "abstinence until marriage" at least once in grades 6-9.
The board said it would discuss Martin's proposal at a later meeting.
Wednesday's vote came less than three weeks after the state Senate approved a bill requiring all school districts to continue requiring sex education classes and prohibit them from going to abstinence-only courses. The bill is now before a House committee.
The board had similar regulations in place for nearly two decades, but they expired.
In November, after a debate that attracted worldwide attention, the board adopted standards that treat evolution as a flawed theory.