Ward Melville High School’s principal issued a letter of explanation Thursday about the school’s decision to have all graduates wear the same style gown — a departure from its longtime tradition of green robes for young men and gold for young women — as a “more inclusive practice” at commencement.

The letter to parents, guardians and students came after a walkout Wednesday by about 100 students at the high school in East Setauket, school officials confirmed, as well as the emergence of online petitions and swirling debate on social media.

The change in graduation garb, to a green gown and a gold stole bearing the high school’s emblem, ignited opinions on both sides of the issue.

The controversy also followed last week’s statements from three top New York officials pledging to uphold the rights of transgender students under federal and state laws and policies that protect them from discrimination and harassment.

Gov. Andrew M. Cuomo, Attorney General Eric T. Schneiderman and Education Commissioner MaryEllen Elia weighed in with those assurances after President Donald Trump’s rollback of the Obama-era directive that instructed public schools to allow transgender students to use bathrooms and locker rooms of their chosen gender.

Graduates file into the commencement ceremony at Ward Melville High School in East Setauket on June 26, 2011. Traditionally, young women have worn gold robes and young men have worn green robes. Photo Credit: Erin Geismar

Ward Melville Principal Alan L. Baum, in his letter about commencement regalia, noted that the Three Village school district is celebrating its 50th anniversary this year and wrote: “On June 25, our district will begin a new tradition, as Ward Melville High School joins a growing list of high schools on Long Island and across the country to provide our graduating seniors with a single color cap and gown.”

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Baum wrote, “It is our hope that creating a unifying color scheme will eliminate the anxiety that is caused by forcing a young adult to wear a gown that labels them differently than how they identify.”

The decision “also reflects the progressive nature of our district, our high school and our community,” the principal wrote. “We are no longer separating students by gender; rather, we will be promoting a more inclusive practice at graduation.”

Opinions of students in the district were divided. Ward Melville has 1,785 students, with 585 seniors in the Class of 2017.

Some petitioned the school to keep separate robes for female and male students.

“For the seniors on graduation day, it is important for us to have different color gowns to walk in. . . . If there are people that identify as a gender other than the one that they received at birth, then they should choose which color they prefer,” the petition read. By Thursday night, it had more than 880 signatures.

Max Gironda, 17 and a senior, authored the petition.

“Personally, for me this has not been about whether students at our school are transgender or not, but rather the fact that a longstanding tradition has been taken from us without notice,” he said.

School officials said the board of education did not set the policy. Informal conversations were held with a group of students late in the 2015-16 school year, they said, and the decision to change to a uniform cap and gown was made recently.

Rachel Keane, 17, of Setauket was among the opposition petition’s signers. The senior said students were never told of the change and only learned through rumors.

“To completely change our 50-year tradition based on the discomfort of a small population of students to pick a color they like best is unfair to the rest of the population,” she said.

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A separate petition, in support of gowns that are the same color, had gathered more than 540 signatures by late Thursday.

“Tradition, as many emphasize, is not always right,” the petition reads. “Allowing everyone to feel comfortable and happy on their graduation day is what is ultimately important.”

Student Karissa Ortiz, 18, a senior from Setauket, was angered by the protest against the change. Some of the students who walked out of school openly criticized the transgender community, she said, adding, “It was horrible.”

Ortiz said she has no issue with the switch. “The new cap and gown — they are really nice and it would make Ward Melville look more unified,” she said.

David Kilmnick, chief executive of the New York LGBT Network, said Thursday his organization has worked with other schools on the Island regarding same-style graduation attire. Paul D. Schreiber High School in Port Washington switched to a uniform style last year, he said.

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“This is a very positive step in the right direction to ensure that all students are equal and safe,” Kilmnick said. “And it doesn’t take away from each student’s unique personality and talent — it is one community moving forward together.”

In August, Ward Melville students had their senior photos taken in either the traditional green or gold robes. School officials said “options are being explored with the district’s photography company” because students now will graduate in a robe of a different style.