“The first month is going to be rocky,” schools reportedly warn parents about their kids’ bus service.

Year after year after year.

Yes, the Department of Education simply assumes it’ll take weeks for routes to smoothen and drop-off times to be met. Don’t dare expect it to go right from the start.

This September, the city’s school-bus hotline has gotten 82,225 calls about late or no-show buses. That’s up from nearly 69,000 complaints in the same period last year.

Queens-based Grandpa’s Bus logged the most complaints from irate parents. It has a $55.1 million contract with the DOE for the year, but four of its routes have already been assigned to another company.

It was a Grandpa’s bus that took 5-year-old Lystra Liu on that tortuous five-hour ride around Queens before dropping her blocks from her stop. On Sunday, her mom shared her daughter’s ordeal with The Post.

Grandpa’s owner, the Logan Bus Co., is ranked nationally among the Top 40 Contractor Fleets. How is it that a major player runs into such trouble in New York?

Chancellor Richard Carranza calls foul-ups “unacceptable.” That word plainly doesn’t mean what he thinks it means.

Bus companies hire drivers with criminal histories and checkered driving records, yet Carranza insists the DOE is on it. “They are vetted, they are fingerprinted, so there’s a process,” he told reporters on Friday. Oh, there’s a process.

That’s the DOE: Buses that don’t show? It’s taking steps. Rising school violence? It’s making adjustments. Schools that don’t teach? It has a program.

Its secret motto: Crappy is good enough.