The parents of a 3-year old autistic child slapped a TriBeCa private school with a federal discrimination lawsuit on Tuesday, claiming their son was denied admission only after being diagnosed with autism.

Jennifer Sample and Eliot Ferguson, of SoHo, said they were elated to learn their the child was accepted into the preschool program at Washington Market School for September, according to the Manhattan federal lawsuit The 55 Hudson St. school has counted the children of Spike Lee, Julian Schnabel and designer Nicole Miller among its alums.

But the couple’s Feb. 28 acceptance letter was rescinded days later when Sample informed school honchos that her kid was recently diagnosed with a neural disorder, the parents said.

Sample and Ferguson said they had been impressed by Washington Market, after touring the campus this past fall and seeing special-needs students – including one child who had a personal classroom aide.

When Sample confronted Washington Market’s director of enrollment, Rachel Macchiesi, the school official said parents of those students never informed administrators “of their children’s special needs prior to acceptance,” according to the lawsuit.

“Accordingly, at least where autism is concerned, it appears that Washington Market follows a practice of ‘don’t ask, don’t tell,'” the suit adds.

Macchiedi, Head of School Ronnie Moskowitz and the school itself were all named as defendants.

Macchiedi and Moskowitz did not immediately return calls seeking their response.

The parents claim their child was never tested by the school – which claims to be “progressive” and doesn’t have admission requirements listed on its website — prior to the rejection, the suit said.

Sample and Ferguson even offered to pay for a one-to-one classroom aide for the child, but they were still rejected.

Only after the parents complained that Washington Market was discriminating against their child, did the school agree to have its “specialist” evaluate the youngster, named in court papers only as “O.F,” according to the lawsuit.

But even after the child did well in the meeting, the school refused to change its position.

The plaintiffs noted that, on this same day, they noticed that renowned autism advocate, Dr. Temple Grandin, was speaking at the school.

“It is at the height of hypocrisy for Washington Market to exploit someone of Grandin’s stature to create the appearance of being autism-friendly when, in actuality, [the school] could not wait to discriminate against our son on the basis of his ‘official’ diagnosis,” Sample said in a statement.

The suit claims O.F.’s civil rights were violated under the Americans with Disabilities Act and the equal-protection and due-process clauses of the Fourteenth Amendment.

It seeks a court order requiring Washington Market staff to be retrained on how to comply with the law, dealing with special-needs students and to hire a court-appointment monitor for at least three years to ensure the school complies with the federal laws.

Additional reporting by Amber Sutherland.