A 26-year-old man climbed on a bus and walked into Stafford High School with students Thursday morning, according to a note sent to parents Friday.
School officials called the man "young-looking" and said that he was believed to be a student before a staff member eventually notified the school resource officer and the man was removed.
He didn't have a weapon and made no threats while on campus, officials noted.
The man reportedly stole food from the cafeteria before being removed.
"It is important to note that the entire incident was handled swiftly," according to the note to parents.
Superintendent Scott Kizner has called for a thorough review and recommendations for any security changes.
"It is obvious that something has to change in our procedures and implemented immediately," school officials wrote. "While this type of incident may be alarming, it is an opportunity to remind our students and staff to remain alert, exercise caution and report any suspicious activity in the schools."