Human error, a system breakdown and a good-faith effort by a bus driver led to a couple of anxious hours for parents and their children Tuesday, as a mini-school bus driver carrying nine kids home from an after-school program in Nesconset ended up getting lost, officials said.

Pledging “a complete review” of the incident, Suffolk Transportation executive vice president Tom McAteer on Wednesday offered “our profound apologies to the families.”

“What happened was we made a mistake and we need to understand how it happened. . . . This is a trained driver. This was a mix up. . . . This was human error. . . . We need to understand this, so something like this never happens again,” McAteer said.

In a note to district parents, James Grossane, superintendent at Smithtown Central School District, called it “an extremely unfortunate and isolated incident,” adding that “none of the children were ever in any danger and were all returned unharmed to their parents.”

According to McAteer and the district, the students in kindergarten through second grade — residents of Nesconset and St. James — were attending a districtwide English as a New Language program at Tackan Elementary School, on Midwood Avenue in Nesconset.

That program lasts 10 weeks, and Tuesday marked the first day of a new 10-week cycle, officials said.

McAteer said the veteran driver, whose name was not disclosed, was given incorrect student and route drop-off lists — lists based on the prior 10-week course cycle at Tackan. He said the driver was issued a new, correct student list on arrival at the school but the new list did not contain a drop-off schedule for the new route.

The driver contacted the company dispatcher, McAteer said, and it was decided, based on the driver’s experience and familiarity with the district, that she would be able to complete the route from memory.

The driver “believed she could do this from memory based on her experience in the district,” McAteer said. In fact, the first of the nine students on board the bus was successfully dropped off at the correct stop before the driver ended up getting lost, McAteer said.

The bus departed Tackan at about 4:15 p.m., McAteer said. Suffolk County police and district officials said a concerned parent called 911 at about 5:30 p.m. to say their child had not yet returned home. Police immediately contacted the school and Suffolk Transportation.

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After a dispatcher contacted the bus driver, the bus was located in St. James and escorted back to the school by police, arriving at about 6:30 p.m., officials said.

The remaining eight children were met by the school principal and safely reunited with their parents.

McAteer said Suffolk Transportation operates between 1,200 and 1,300 buses and vans serving 16 districts and about 25,000 children in Suffolk on a daily basis. He said Wednesday he can’t recall a situation like this one ever happening.

“Ultimately, it’s human error,” McAteer said. “Fortunately, this is a very, very rare occurrence. It’s a rare occurrence because any time something like this happens we review the situation, try to understand where things went wrong, and figure out how to make sure they don’t happen again.”