Meriden — Kimball Union Academy has received a gift of $20 million to its endowment, the largest in the 206-year-old boarding school’s history.

KUA said the donor wished to remain anonymous, but the school said in a Wednesday news release that it was a “transformative gift” that was “a testament to the impact the school has on the lives of its students and community.”

The Meriden-based school was established in 1813 and has 340 boarding and day students in grades 9-12.