"No one at the school had written about this."
Translation:Nadie en la escuela había escrito sobre esto.
Singingypsy and anticorncob28, I guess we won't get an answer to our question. It's pretty annoying not knowing when to use SOBRE or DE as it seems they are being used interchangeably! Please refer to a question in this module "We had agreed not to talk about that anymore" DL translated as "NO HABLAR MAS DE ESO. I rest my case.
Duo doesn't accept "nadie de la escuela", which I think is how Spanish speakers tend to think about such phrases... We're not really talking about someone located at the school, but rather someone belonging to the school. Duo defaults the other way with "the trees in the park" as "los arboles del parque". As a similar phrase my grammar books give "the men in Greece" as "los hombres de Grecia". But then maybe Duo really does mean "located at".