The incident happened Friday afternoon at Leroy Drive Elementary.
According to a letter sent out to parents, three students told school staff members they saw a man off school property expose himself.
"This individual was far from our students and he had no interaction with them. Staff immediately brought the students in from recess, and called the Northglenn Police Department and district security," Principal Jill Roth said in the letter. "As a precaution, we canceled recesses that were scheduled for the rest of the day."
Roth says police and school staff worked with the students who saw the incident to gather information and to support them.
"This is a good reminder to talk to your children about reporting any concerns they may have about their safety or the safety of others to a trusted adult," Roth said.
If you have any information on the case, contact Northglenn police.