This is really “old” school.

A 32-year-old woman has been arrested for posing as a homeless 15-year-old to try to enroll at a upstate New York school, cops said.

Michaelann Goodrich was busted after attending one day of classes on Dec. 20 in the Cairo-Durham district under the name “Riley Madison,” according to local network WNYT.

Goodrich rode the bus to and from school that day but was absent the next. Winter break began the following week.

Superintendent Anthony Taibi said something felt wrong, so school officials called cops.

“We notified law enforcement immediately,” he told HudsonValley360.

Under a 1987 federal law called the McKinney-Vento Homeless Assistance Act, the district, which is near the Catskills, was required to immediately enroll Goodrich even if she didn’t have proper documentation.

The act protects homeless students to ensure they receive the same educational opportunities as other students. It also awards federal grant money to local districts.

Taibi said he didn’t know if Goodrich suffered from mental health issues. He said she was under adult supervision while in the school, as part of school procedure.

“I don’t know what her motives were,” Taibi said.

The investigation into Goodrich was completed before school reopened Wednesday following the break. Police are working to figure out whether Goodrich made similar attempts to falsify records, enroll at other schools or access children.

She was charged on Dec. 28 with offering a false instrument for filing, falsifying business records, and criminal trespass and held in jail on $5,000 bail.

Joel Rowell, a senior investigator with the Greene County Sheriff’s Department, said the woman has a high school diploma, so it’s unclear why she wanted to enroll.

“She could’ve gone in numerous different ways to obtain a degree and we actually found out through the investigation and that she has a high school diploma,” Rowell told WNYT. “So that just leads to our investigation to try to figure out what exactly her motive was for attending school.”