Joseph Denice, 24, was a volunteer religious instructor at the Saint Mel School in Flushing.
He allegedly used Facebook to contact a minor, which is against school policy.
The child's parent contacted school officials on December 31 about the alleged contact, and Denice was let go on Monday.
The Queens district attorney's office says Denice is a registered level-one sex offender who now lives on 15th Avenue in Whitestone.
Officials say he spent six months in prison in June for sexually abusing a 12-year-old boy between July to September 2009. The victim was in the afterschool program where Denice worked.
According to the district attorney, Denice forged letters from judges saying the boy had to have a "body scan" as part of an investigation by the Administration for Children's Services. Denice then performed several "body scans," which involved sexually touching the boy.
The Brooklyn Diocese said every volunteer goes through intensive training and a background check, and a diocese representative said a check was done on Denice in 2005.
However, no background check was made when Denice recently returned from prison.
One parent of a sixth-grade student at St. Mel’s School was in Flushing could not believe Denice was allowed to work with children.
"That's horrible," said parent Rita Ivrillo. "I have one boy in that school now, in the sixth grade, so it's horrible. I'm sorry to hear that. I'm outraged."
Nicolette Tricomi, a neighbor, has known Denice since he was a boy and even had him babysit her children.
"I'm shocked, it's hard for me to believe," she said.
NY1 spoke to Denice over the phone but he made no comment.
The station also contacted the rectory at St Mel’s, which had no comment.
In a statement, the Brooklyn Diocese says it is evaluating how to prevent a similar situation in the future and determining whether it needs to re-screen some of its volunteers.