The Rockville Centre school district overpaid 44 current and former teachers about $250,000 over the past three years and is working to recover the funds, the board of education announced in a statement posted Tuesday on the district's website.
Business office staff discovered the mistaken payments in early September while questioning the payroll of some employees, Superintendent William Johnson said.
The district's legal counsel is investigating the matter.
The overpayments were about $83,000 in each of the three years, starting with the 2011-12 school year.
"The board wants a complete explanation, and it is a mystery to me -- with all the controls we have in place -- that something like this could happen," Johnson said.
District officials said a mistaken execution of the collective bargaining agreement between the teachers' union and the district may have contributed to the error.
The teachers are working under a four-year contract that runs through the 2015-16 school year, Johnson said.
"There was a clause in the contract that was . . . as best as I can see at this point, honestly misinterpreted," he said.
Viri Pettersen, president of the Rockville Centre Teachers' Association and a full-time teacher in the district, said in a written response that the association "is aware of the issue. We are currently gathering the facts. When all the facts are clear, we are going to be discussing with the school district how to resolve this issue in a way that's fair to teachers, fair to retirees and fair to taxpayers."
Johnson said he has met with the union and the affected employees and is setting up a meeting with the retirees.
The error, which began with the 2011-12 academic year, was corrected before the first paychecks of the current school year were distributed, officials said.
The district's legal counsel is assisting the board with recovering the funds, which could be done in a "variety of ways," Johnson said.
All of the teachers who received the payments either are or were senior faculty members who had topped out of the current step-increase schedule, according to the statement.
"The Board of Education is deeply concerned about the error," read the statement. "We are also concerned that this error was not discovered sooner by internal staff or those who provide external support to the district's business function."
Data from the 2012-13 New York State Education Department, the most recent figures available, showed that the district employed more than 320 teaches and served about 3,500 students.
"This is an unfortunate situation and we offer our apologies to the taxpayers," the board's statement said.