For the second time in two weeks, a Philadelphia first-grade student found himself alone, abandoned, in an empty city school bus after he fell asleep on the way to school Wednesday and no one noticed.

The 7-year-old, who attends a private school in West Philadelphia, woke up scared and disoriented in the hot, locked bus, his parents said. By midday, police and the School District were investigating the incident.

On May 29, the same boy had an identical experience, when he was left on an empty bus for four hours and discovered only after his frantic parents made calls to their school, Quba Institute, to try to find their son.

This time, the boy, Atif Ibn-Kayzar, was left on the bus for perhaps 90 minutes, said his father, Kayzar Sanders. Atif had fallen asleep again, and despite promises from All City Transportation Co., the driver did not check the bus before leaving it, Sanders said.

Police would not confirm an investigation Wednesday or that they took the unnamed driver into custody. Lee Whack, a spokesman for the Philadelphia School District, which is responsible for transportation for nonpublic students, said that "overseeing the safe transport of our students on a daily basis is one of our most important responsibilities."

Drivers must follow district procedures, Whack said, and "falling short of those standards is unacceptable." He said the district was working with All City and the police to look into the matter.

A person who answered the phone at All City Transportation, which is based in Southwest Philadelphia, said:  "The situation is under investigation, they're trying to get to the bottom of everything." She declined to say more.

Sanders said the All City driver parked the bus outside of his home after making his morning run, not knowing the boy was asleep in the back. When Atif woke up, he grew upset and banged on the bus window, his father said.

"Some ladies were walking past, and they told him to lower the window," Sanders said. "They said, 'Are you all right?' and he said, 'I don't know where I am.'"

The neighbors called police, who took Atif to their station and called his incredulous and frantic parents.

"I couldn't believe it," said April Silver, Atif's mom. "I feel horrible that my son had to go through this again."

She said the driver who left her boy on the bus last month was a substitute and was fired after the May incident, and that she and her husband received assurances from All City that such an error would never happen again.

"They were apologetic," said Silver. "They said in all their years of operation, that had never happened."

After that first incident, Atif couldn't understand why no one had awoken him and was afraid to go back on the bus, his parents said. But they convinced him it was safe to ride again, they said, in part because he knew his regular driver, a well-known presence and a man they call Mr. Joe.

"He's 7 — he was scared," Sanders said. "I said, 'You've got to be a big man, you've got to take the bus. It's OK as long as Mr. Joe is the driver.'"

The driver had been caring for his wife, who was ill. He apparently parked the bus outside his home between school runs.

The School District frequently contracts out bus routes, and has run into trouble with vendors in the past. There is a national shortage of school bus drivers.