The Oakland-based Environmental Working Group says over three million school absences a year are attributed to pollution-related maladies like asthma.
School officials in San Joaquin County say they believe about 20 percent of their students suffer from such ailments.
To cut down on absenteeism, especially on so-called "bad air days", district spokeswoman Sherie Coburn, says affected students are kept in doors.
"We make modifications so that they're not outside playing. We encourage teachers to do other physical activities either in the gym or inside the classroom."
Bill Walker of the Environmental Working Group says if California is serious about education it should adopt stricter air quality guidelines.
"Let's take a look at the whole environment the child is in, not just the teaching environment."
Walker says pollution-related absences cost schools hundreds of thousands of dollars a year in lost reimbursements from the state.