Two pupils, a 16-year-old boy and a 14-year-old girl, died in Wednesday's avalanche at the Deux Alpes ski resort, as did a 56-year-old Ukrainian tourist.
The sport teacher from a school in the central French city of Lyon took the group onto the piste, even though it was closed off with netting and signalled by warnings in four languages, prosecutors say.
"He recognises his responsibility, he is not in denial. He did not realise the danger because many people had taken this piste over the previous two days," lawyer Benedicte Tarayre told the AFP news agency, adding that he was "shocked" and "angry" by the tragic turn of events.
He is forbidden to leave France or to practise his profession.
The teacher had ended hospital treatment for severe depression in November and was taking heavy medication.
He has admitted going onto the piste the day before the accident.
The Bellecombe piste is rated a black piste, France's highest difficulty rating, and had been closed for lack of snow.
But there had been heavy snowfall in preceding days, leading to a warning of a high danger of avalances in the French Alps.
The risk level at the resort on the day of the accident was three on a scale of five, meaning a single skier can set off a landslide.
Charges could also be laid against the school, local authorities, the ski station or skiers who set off the avalanche, if they are identified.
A group of Hungarian tourists, some of whom have already been identified, passed through the area above the avalanche just before it took place on their way to another piste.