The San Francisco Sheriff's Office says it was conducting an indoor training with the chemical agents at the San Bruno jail.
Somehow, the sheriff's office says the tear gas from the training wafted outside and all the way to the school - a mile away.
Children and teachers felt the burning in their eyes, nose and throat.
The sheriff's office says this has never happened before in 20 years of training at that location.
The San Francisco Sheriff director of communications told us in a statement: "We sincerely apologize to Portola Elementary School, its faculty and students, and their families for this unforeseen event which must have been especially scary for children."
They're pausing all training with chemical agents.