BOSTON — Board of Elementary and Secondary Education Chairman Paul Sagan is defending his decision not to reveal a $500,000 donation he gave to a New York-based group pushing last year’s charter school ballot question.

In a seven-page statement, Sagan said it was up to the group, Families for Excellent Schools-Advocacy, to reveal the donation — not him.

Sagan said he considered publicly disclosing the gift —and a second donation to another pro-charter school group — but decided against doing so.

“Why? On balance, I thought that if I went ahead and announced my donations, opponents of Question Two would accuse me of using my position as chair of the Board of Elementary and Secondary Education as a platform to help influence support for expanding the statutory cap on charter schools,” Sagan said in the statement.

Sagan, who read the statement during a board meeting Tuesday, said he checked with the State Ethics Commission last year before making the donation.

He said received a written response advising him that under the state’s conflict of interest laws, his position as board chairman didn’t bar him, or his wife, from contributing personal funds to any political campaign or advocacy group.

He said he sent a disclosure letter to Republican Gov. Charlie Baker in September 2016.

Sagan also said in the statement that he made it clear to pro-charter school groups that he “would not help them with fundraising and they could not use, or even reference, my involvement with the Board of Elementary and Secondary Education in any of their activities, specifically because I did not think that would be appropriate.”

Sagan’s donation was only disclosed earlier this month after an investigation by the state Office of Campaign and Political Finance forced Families for Excellent Schools-Advocacy to release the names of its donors and pay a record $425,000 as part of a campaign finance settlement.

Investigators said the group raised more than $15 million from individuals and then contributed it to the Great Schools Massachusetts Ballot Question Committee in a manner intended to disguise the true source of the money.

The money represented 70 percent of the $21.7 million reported received by the charter school committee. During the campaign Families for Excellent Schools-Advocacy did not respond to requests to reveal their donors.

Voters ultimately rejected the ballot question, which would have lifted the state cap on charter schools.

Baker, who appointed Sagan to the post, was an enthusiastic supporter of the initiative, appearing in television ads for the ballot question.

When an earlier donation of $100,000 by Sagan was revealed last year to a separate pro-charter school ballot question group, Baker quickly dubbed criticism aimed at Sagan “a nothing-burger.”

Questioned by reporters after it was revealed that Sagan had made an additional $500,000 gift, Baker said there was nothing wrong with the donations.