More than 600 students were not allowed into class today in Windsor-Essex due to incomplete immunization records.
The suspensions went out to 659 students born from 2008 to 2011.
Parents will need to bring proof of immunization or a valid exemption to the health unit and get a form to allow the child to go back to school.
Walk-in clinics are available to get the records updated.
At the beginning of the school year, 2300 letters were sent out to parents warning them about the suspension notice.