The 29-year-old woman pleaded guilty to the charge at Sarpsborg district court on Tuesday.
Speaking to the court, the boy described how he felt the teacher had begun to fall in love with him, broadcaster NRK reports. One night last summer, the pair shared a bed in a cabin during a class trip.
According to the boy, the teacher asked him if he would like to have sex with her. He said he lay awake all night thinking about the offer before giving his assent the next morning.
Afterwards, the boy said he felt let down by his teacher and had trouble sleeping.
The woman was deeply affected by the boy's testimony on Tuesday and looked in the opposite direction throughout the hearing, NRK reports.
Addressing the accused, prosecutor Arild Eikaas recommended that she be barred from teaching for a period of five years. He has also called for the woman to pay the victim compensation.
Local authorities first reported the teacher after rumours began circulating around the school and on Facebook.
The teacher did not return to work after the 2011 summer holidays.