An incident where a 5-year-old boy remained unnoticed on a school bus left at the school bus barn in Gardiner has triggered an investigation by the school district.

The boy was spotted as he was walking alone along U.S. Route 201 — also known as Brunswick Avenue — about 4:30 p.m. Tuesday, apparently trying to get home.

Gardiner Police Chief James Toman said Wednesday that the boy was walking south on Brunswick Avenue, also known as Route 201, when he was spotted by “a good Samaritan” about 4:40 p.m. The bus barn is on Brunswick Avenue near Pushard Lane.

The boy was given a ride home by Officer Samuel Quintana.

The incident has triggered an investigation by Maine School Administrative District 11, the Gardiner area schools, according to Superintendent Patricia Hopkins.

“This is the type of event that every superintendent dreads,” Hopkins said via email Wednesday. She said she learned of the incident Tuesday evening. “I became aware that a young elementary student was not dropped off at his home and was left unaccompanied on a school bus at the bus barn.”

She also said, “I can assure you that the school district has taken this matter extremely seriously and has initiated an investigation. To the extent that its cause may lie with an employee, by law, I cannot comment on what actions might be taken. I can guarantee however that there will be a thorough review of all our practices to ensure that this does not happen again.”

She added, “Both the school board and the administration make great efforts to ensure that the students entrusted to our care are safe,” Hopkins said. “We have enacted protocols and practices to prevent the exact situation that occurred late yesterday afternoon.”

She said drivers are expected to check buses before leaving them at the school bus depot, a protocol “clearly outlined in the bus driver handbook.

“The student fortunately made it home safely due to the intervention of a concerned citizen and the police,” she said.

Betty Adams — 621-5631

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Twitter: @betadams