The California Department of Education requires students to take fitness tests in grades five, seven and nine.
Part of the test includes a screening for obesity through a body mass index text.
The department requires students are required to receive the results of their tests, and some districts choose to let the parents know as well -- through what have been called "fat letters," CBS News reported.
The National Eating Disorder Association said it is worried the letters will cause students to begin exhibiting unhealthy behaviors, like skipping meals.
But some school district officials said the letters help inform parents about their children's health.
Obesity rates have more than doubled in children and tripled in adolescents in the past 30 years, the Centers for Disease Control and Prevention said.
Massachusetts previously required BMI screening for students and required letters be sent home, as well.
The state reversed its position on the "fat letters" in October, CBS News said.