NARRAGANSETT, R.I. (WPRI) — An investigation is underway after a 6-year-old student was unintentionally left alone on a school bus in Narragansett last week, 12 News has learned.

Narragansett Superintendent Dr. Peter Cummings said in a statement Monday afternoon that the bus driver has been let go for "failing to uphold safety standards."

Cummings said the "unfortunate incident" happened at the end of the morning bus run, which is when the driver is supposed to ensure that all students have safely exited the bus. The student was left alone on the bus for approximately 20 minutes before being noticed.

"We deeply regret this incident and understand the distress it caused," Cummings wrote. "The safety of our students is our top priority, and we have taken immediate corrective action."

Brenton Butterworth told 12 News the student left behind on the school bus is his daughter. He said his daughter fell asleep on the bus on her way to Narragansett Elementary School Thursday morning.

"How do you leave a 6-year-old that's sleeping on a bus that has a limited amount of students to begin with?" Butterworth questioned.

Butterworth explained that the driver who left his daughter on the bus was a substitute and not her regular driver.

"She does have a normal driver that she has a very good relationship with," Butterworth said. "We feel comfortable with him and he feels comfortable with us."

Butterworth hopes to obtain a copy of the surveillance footage from the bus so he can see exactly what happened.

Though his daughter is doing well, Butterworth said he's worried about how this will impact her long-term.

"She does have some learning disabilities ... so her comprehension and understanding of this scared me quite a bit," Butterworth said. "Even if something doesn't bother her today, it could bother her three months from now. It comes out of the blue."

Cummings said the district is reviewing its protocols and are reinforcing them "to ensure this does not happen again."