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."

Saracens full-back Goode, who has a minor ankle injury, is England's only concern following the 40-9 win over Italy on Sunday.
After winning their first two games, England now have a weekend off before facing Ireland on 27 February.
Bath back Devoto, 22, is uncapped, but was an unused replacement in the opening win against Scotland.
He was dropped from the 23-man match squad against Italy when head coach Eddie Jones opted for a six-two split between forwards and backs among the replacements, with Maro Itoje coming on to the bench and subsequently winning his first cap.
England training squad:
Backs: Mike Brown (Harlequins), Danny Care (Harlequins), Ollie Devoto (Bath), Owen Farrell (Saracens), George Ford (Bath), Alex Goode (Saracens), Jonathan Joseph (Bath), Jack Nowell (Exeter), Anthony Watson (Bath), Ben Youngs (Leicester).
Forwards: Dan Cole (Leicester), Jack Clifford (Harlequins), Jamie George (Saracens), Dylan Hartley (Northampton), James Haskell (Wasps), Paul Hill (Northampton), Maro Itoje (Saracens), George Kruis (Saracens), Joe Launchbury (Wasps), Courtney Lawes (Northampton), Joe Marler (Harlequins), Chris Robshaw (Harlequins), Billy Vunipola (Saracens), Mako Vunipola (Saracens).
Sixteen teenagers on a Spanish exchange programme were among those on board a Germanwings plane that crashed in the French alps, German officials say.
[NEXT_CONCEPT]
Ollie Devoto will train with England as injury cover for Alex Goode before the Six Nations match against Ireland.