Add “rubdowns” to the three R’s.

A high school principal was yanked from his post after rewarding a dozen staffers with a spa day at a notorious Queens bathhouse that has been likened to “the set of a porn movie,’’ The Post has learned.

While other employees at Harlem Renaissance High School were forced to spend Monday, Jan. 30, at school — for a citywide “professional development’’ day ordered by Chancellor Carmen Fariña — their 12 lucky male and female colleagues frolicked at the three-story Spa Castle.

The Post reported last year that the spa was infamous as a sex den on weekends, drawing after-hours strippers and other randy patrons.

The chosen-few school workers were pampered at the College Point establishment while on the clock — with their salaries covered by city taxpayers.

The group included the school’s assistant principal, dean of students, teachers and other support staff favored by principal Nadav Zeimer, according to internal documents obtained by The Post.

The staffers were singled out by Zeimer for their “exceptional service,” which included such lofty achievements as “Never Late!” “No Days Absent” and “Hungry for Feedback,” according to one memo.

As part of their special day, they were asked to spend an hour-and-a-half in silence contemplating such heady questions as, “Why are we here?” and “What is reflection?,” another document shows.

Meanwhile, their co-workers had to show up at the East 128th Street school at 9:30 a.m. for a full day of administrative work.

Last year, the school had a mediocre graduation rate of 56 percent and an even worse college readiness figure, 29 percent, according to the Education Department.

When one of the left-behind staffers dared to ask Zeimer about the spa trip, he snipped in an email, “I am taking care of the cost of the retreat . . . Rest assured that no school budget is being used,” not saying where the money was coming from.

Spa Castle charges a $40 entrance fee on weekdays, which would amount to at least $480 for the outing. Zeimer made sure to ask the rogue worker not to go above his head, the email shows.

The DOE launched an investigation into the incident — and reassigned Zeimer — after an inquiry by The Post.

“The goal of training teachers and staff is better instruction in the classroom, and we have referred this matter for investigation,” a DOE spokesman said.

Zeimer did not return requests for comment. Last month, he landed at the center of a lawsuit for allegedly pressuring staffers to pony up hundreds of dollars for self-improvement courses.

A spokesman for the spa told The Post, “Spa Castle is a safe, family-friendly center that strictly enforces policies against improper dress or behavior.”

Additional reporting by Selim Algar