That's because some children like 5-year-old Bailey Lynn can't get vaccinated. She was born with a spinal defect. She can't walk. She can't sit but her mother, Nicki Chintala, says she doesn't allow her disability to hold her down.
"She's happy. She's had a lot of issues, a lot of surgeries. But she's happy. And she likes school," said Chintala.
And next year, Bailey Lynn will go to kindergarten.
Due to her many medical issues, her immune system is compromised. She can't get the measles vaccine, putting her at risk. And that has mom concerned.
"Her choice has been taken away and I don't think it's fair for other people to say my body my choice, she doesn't have it," Chintala says.
There are no US Federal vaccination laws. Pennsylvania, New Jersey and Delaware allow exemptions for medical and religious reasons. Pennsylvania also allows philosophical exemptions.
Statewide, all three states are above or near the 95% threshold health experts cite for herd protection, but Action News found 33 percent of schools are below that figure in New Jersey.
In Pennsylvania, 13% are below the threshold.
Delaware does not provide vaccination rates at the school level. Of the 30 schools with the lowest MMR vaccination rates in the keystone state, we found more than half are in Southeastern Pennsylvania.
Dr. Kristin Feemster is the director of the Immunization Program at the Philadelphia Health Department.
"If you're at a school and your immunization rate is let's say 80%, as a parent, should you be concerned? Yeah, absolutely," said Feemster
Long Island Mother, Cathy Orofino, doesn't want the government telling her what goes into the bodies of her three boys. New York has been hit hardest by the measles outbreak and recently banned students who have not been vaccinated due to religious reasons.
"I just believe that they are born with a God-given immune system. I believe that it is sacred and not interfered with by man."
Orofino may soon have to make a tough decision: home school her kids or get them vaccinated.
Both New Jersey and Pennsylvania lawmakers have considered similar legislation.
Nicki Chintala supports such legislation, but for now, she'll focus on deciding what's best for Bailey Lynn's education destination.
"Homeschooling was something we talked about and it still might be an option if it comes down to it.
When the measles outbreak happened, all I kept thinking about is "Oh my God, if she catches it, her survival rate is low."
Measles in NYC: WABC investigates vaccination rates in New York, New Jersey and Connecticut.
Measles in Los Angeles: KABC investigates vaccination rates in Los Angeles County and California.
Measles in Chicago: WLS investigates vaccine rates in Illinois and Indiana.
Measles in San Francisco: KGO investigates vaccination rates in nine Bay Area counties.
Measles in Houston: KTRK investigates vaccine rates in Texas.
Measles in Raleigh-Durham: WTVD investigates vaccine rates in North Carolina.
Measles in Central California: KFSN investigates vaccine rates in six California counties.