After Sheila Sustrin died on Monday at age 76, her identical twin sister, Letty, placed a copy of their latest children's book, "The Teacher Who Would Not Retire Loses Her Ballet Slippers," into her coffin.

The Deer Park sisters -- both retired elementary school teachers -- wrote five children's books together about retired schoolteacher Mrs. Belle, who always wears ballet slippers. "She dedicated her life to children," Letty Sustrin said of her sister, who died after battling cancer for years.

The twins worked side by side for 38 years in the Brentwood school district, 18 years teaching kindergarten at Northwest Elementary, now called the Freshman Center, and 20 years teaching first grade at Laurel Park Elementary. They were known for dressing identically, but each would wear individual jewelry such as a pin or a necklace or a ring with her first initial.

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Both took early retirement in 1998, and in 2002 they published their first book, called simply "The Teacher Who Would Not Retire." Subsequent picture books in the series, aimed at children ages 4 to 10, included "The Teacher Who Would Not Retire Goes to Camp," "Discovers a New Planet" and "Becomes a Movie Star." The last two books were launched at the YMCA Boulton Center for the Performing Arts in Bay Shore.

Neither twin married, and they lived together. "We got married to our jobs," Letty said. "The kids became our kids."

Indeed, one former student who lives in Texas wrote this about Sheila on Legacy.com: "Letty, having you and Sheila as my 1st teachers has made such an impact on my life. . . . Sheila will be greatly missed by countless people whose lives are better for having you and her as our teachers."

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The Sustrins visited Long Island schools to read from their books and were so involved with their second career that they named their Scottish terrier Belle after their protagonist. Letty said she's not sure if she will carry on the series alone. "This is something I have to think about," she said.

In addition to Letty, Sheila is survived by a cousin, Marilyn Weissman of Sanford, Florida. Donations can be made to the North Shore Animal League, Little Shelter in Huntington or Bideawee in Wantagh.