The earlier starting date is necessary in part because many girls are exposed to issues of sexuality at a younger age, said Judy Robinson, executive director of the group based in Scarborough, Maine.
"You'd be amazed at what kids are asking these days," she said. "They want to know about (sexual) positions."
Generally, children in the United States receive sex education in the fifth grade.
For the past three decades, the accepted belief was that puberty started between ages 10 and 12. But a 1997 study by the American Academy of Pediatrics suggested it can begin for girls as early as 8.
Girls who develop early -- or who teachers observe using more sexual language or behaving in sexual ways -- could be selected to take the fourth-grade classes, Robinson said.
Under the plan approved by the association's board on Thursday, parents could choose to exclude their children from the fourth-grade class.
Sandy Gadsden, a board member of the nurses group, said the proliferation of sexual images in popular media is another reason for teaching girls at a younger age.
"Children are surrounded by sexual messages, and not all of them are healthy," Gadsden said. "It's important to establish a baseline of information so girls can evaluate all the messages."
In addition, Gadsden said, early education about puberty can help reassure girls who may be harassed if they develop earlier than their peers.
"Young girls need to be armed with understanding and knowledge to be assertive that their body is their own," she said.
But some parents and educators questioned whether a girl still playing with Beanie Babies has the emotional maturity to deal with such issues.
Roxanne Flores, a Providence mother of a 1-year-old daughter, said a fifth-grade puberty talk sounded appropriate to her. "A fourth-grader doesn't understand anything," she said.
Marsha Campbell, a health education specialist at the state's Department of Education, said the difference in girls' maturation makes it difficult to say whether all fourth-graders could handle learning about puberty.
"It would be foolish and misleading to say they are all ready or they all aren't," she said. "Everyone's different. You have to know your community, and you have to know who you're teaching."
Written By Gina Chon