A married teacher fled to France with a teenage pupil the day after police questioned her about the nature of their relationship, a court has heard.
Jeremy Forrest, 30, and the girl, who cannot be named, took a cross-Channel ferry to Calais before spending seven days on the run.
His behaviour was a "gross breach of trust", Lewes Crown Court was told.
Mr Forrest, who taught at Bishop Bell C of E School in Eastbourne, denies child abduction.
Richard Barton, prosecuting, told the jury: "This is not Romeo and Juliet; this is a 15-year-old girl with her own vulnerabilities, and a 30-year-old teacher.
"When parents send their children to school, they quite properly expect that those who teach their children will care for them properly."
He said the girl willingly fled the country with Mr Forrest but that could not be used as a defence to the charge of child abduction.
He added: "The girl would tell her mum that she was at a friend's house.
"Jeremy Forrest also lied to his wife about where he was at these times but in truth they were meeting up locally at a Premier Inn and the White Hart across the road from the court, purchasing rooms so that they could be together."
Jurors were told police were tipped off by a "third party" about their relationship and pictures Mr Forrest is claimed to have sent the girl, on September 14, six days before they left the UK.
A few days later Mr Barton said a police officer and social worker questioned her at her house about the nature of their relationship and seized her mobile phone but she denied improper contact with the teacher.
He said knowing they would be discovered from the content on her phone, the girl secretly packed some clothes and a passport and Mr Forrest booked ferry tickets in the name of J Forrest and E Forrest.
The court heard the pair used aliases on false CVs to try and get work at an English bar in the French city of Bordeaux but the owner recognised them from newspaper reports and they were caught on 28 September.
The jury was also played a video from 3 October which showed the girl telling a police interviewer their relationship developed from holding hands on the way back from a school trip to Los Angeles to a sexual relationship.
"I asked a friend to get his number and we began texting for all of April and all of March," she said.
'Got more serious'
"The texts started off with a lot of kisses. When we first began texting, we were gradually getting more like into a relationship, and there were photos and stuff like that, and there were other text messages.
"But we didn't start a relationship until the end of May and we decided that it was what we wanted to do. Around this time, we began to meet up outside of school.
"There were a few times when I would go over to his house... and after that things got even more serious."
The prosecution told the jury Mr Forrest was repeatedly warned to discourage the girl.
The trial of Mr Forrest, of Chislehurst Road in Petts Wood, south-east London, is due to last two weeks.