The group, and two teachers, were from Joseph-Koenig school in Haltern, western Germany.
"This is the worst thing imaginable," the town's Mayor Bodo Klimpel said at an emotional media conference.
All 150 people on board flight 4U 9525 travelling from Barcelona to Duesseldorf are assumed to have died.
The Airbus A320 airliner went down between Digne and Barcelonnette. The cause of the crash is not known.
Most of those who died from the school were girls aged about 16, an official told the BBC's Katya Adler.
Students at the school in Haltern were sent home for the day, but some returned to lay flowers and comfort each other.
Mr Klimpel confirmed that the group was on the passenger list and said he was informed by the Spanish school they had boarded.
He said the school would still open on Wednesday, but instead of normal lessons there would be "an opportunity for the pupils to talk about this terrible [tragedy] and begin to process this".
The group had been participating in a week-long exchange at a school in Llinars de Valles, near Barcelona. Their Spanish counterparts visited late last year.
Tributes have been paid.
"They were flying home after having what was probably the most wonderful time of their lives," said Sylvia Loehrmann, the education minister for the state of North Rhine-Westphalia.
"It's so tragic, so sad, so unfathomable."
German international footballer Benedikt Howedes, who was born in Haltern, tweeted: "Our thoughts are with the victims and families of the tragic airplane accident. Anyone could have sat on that machine."
Sixteen teenagers on a Spanish exchange programme were among those on board a Germanwings plane that crashed in the French alps, German officials say.