Twenty-four-year-old Patricia Gallegos of Rutherford faces child endangerment charges.
Bergen County prosecutors say Gallegos had engaged in sexual conduct with the boy on several occasions since last month. But none of the incidents occurred at the Robert L. Craig School in Moonachie, where Gallegos was a substitute for about a year.
School administrators notified authorities upon learning of the allegations on Thursday, and Gallegos was arrested Friday. She was then fired.
Bail was set at $20,000, but it wasn't clear whether Gallegos remained in custody Saturday. A telephone number for her could not be located, and it wasn't known if she had retained a lawyer.