"In our school, nothing is as it was before," Joseph-König-Gymnasium (secondary school) headmaster Ulrich Wessel told journalists gathered in the town in North Rhine-Westphalia.
"A week ago on Tuesday, we sent 16 happy young people with two happy young colleagues on a trip, an exchange with a school we've been linked to for six years."
One of the teachers had been married just six months ago, he added.
He said that everyone at the school was grateful for the messages of support from across Germany and abroad, and would be supporting each other through the coming days.
"I have tried to put the school on the right path, in close agreement with the headmaster," North Rhine-Westphalia schools minister Sylvia Löhrmann said.
She added that 50 counsellors and psychologists were on the scene to offer support to pupils and staff, who had lost close friends.
She said there would be an official minute's silence across the state at 10:53am on Thursday morning, the time the plane went down on Tuesday.
"I hope that many schools and pupils, teachers, will use this opportunity to exchange and to mourn together.
"All of Germany is mourning and we are getting messages of empathy from all over the world," she added.
“Yesterday we were many. Today we are alone,” a message read on a board outside the school, which lost 16 pupils and two teachers in Tuesday's Germanwings plane crash.