Gill Bremner, head of Wilmslow High School, where Hannah Thomas-Jones was a Year 9 student, said she would be "sadly missed" by pupils and teachers.
She said: "Hannah's death is a very sad loss for this school. Our sympathies go out to her family at this time after such a tragic incident."
More top news
Claire Lomas was greeted by cheering supporters after walking through the night to make it to the finish line.
The boy matches no missing persons profile and police say they have yet to find any clues as to his identity.
The prime minister told MPs she was hopeful 'sufficient progress' would be made to move talks on to trade by December.