The school district doesn't know what the particular illness is, however, parents with sick kids told FOX40 symptoms include vomiting and diarrhea.
The school district's superintendent Denny Rush says the school went through an intensive disinfectant process after school Thursday and that common area classes like Spanish and music have been moved to classrooms, so as not to bring in more students to an area where the virus may have originated.
Mark Aday says his son is a kindergartner at the school and that many of his classmates are sick as well.
"He was vomiting a lot this morning and he looked pretty pale but I think he's fine now," Aday said.
The Newcastle Elementary School District says that it is working closely with the Placer County Health Department to figure out what exactly is causing so many students to get sick.