Your request seems so simple, but it's quite a challenge! I think these may fit the bill:
13 LITTLE BLUE ENVELOPES by Maureen Johnson
FEELING SORRY FOR CELIA by Jaclyn Moriarty
THE DECLARATION by Gemma Malley
THE HOUSE OF THE SCORPION by Nancy Farmer
HOLES by Louis Sachar
THE SCHOOL FOR DANGEROUS GIRLS by Eliot Schrefer
If these do have romance, I'm fairly certain that it's not the main part of the novel. I just went through my goodreads to find this list; a lot of these I haven't read in ages.