Diane Pullar, a primary school playground assistant allegedly groomed the boy after her son made friends with his older brother, and the two families became close; she began picking him up from school and also sent him secret texts, the Cambridge Crown Court heard.
Pullar is accused of having sex with the boy at least five times, and committing another sexual offence, the 'Daily Express' reported.
Prosecutor Claire Matthews was quoted as telling the jury, "Diane Pullar was involved in a full-blown sexual relationship with a child. The families became close and even went on holidays together. Diane knew his age because she went to his 13th birthday party and bought him a card.
"She attended the party after abusing the boy. She would collect him from school in her car. Sometimes he would miss school with her encouragement, and meet for sexual reasons. "Diane told him, 'You cannot tell anyone or we will get into really bad trouble'."
The relationship was exposed when a teenage boy walked in on the two while they were apparently having sex.
Matthews continued: "Another friend's son visited Pullar and was allowed to let himself in. One day he remembers knocking on the door and there being no reply. He let himself in and saw her and the victim on the sofa together."
However, Pullar, who worked at Glebelands Primary School in Chatteristhough, has pleaded not guilty to all the six charges of engaging in sexual activity with the child between April and July 2009.
Pullar, who was earlier arrested, told the police that the incident was a "mistake" and told the victim's mother: "He has a crush on me, it's sweet," the report said.
The trial continues.