Other charges in the case include witness tampering and juvenile possession of a firearm.
The boys had created a handwritten plan which included raping the classmate before stabbing her to death. The prosecutor said one of the children "described rape as a display of strength and power — not sex."
Another student saw the knife fall from one of the boy's backpacks as he was getting on the bus and reported it to a teacher. In addition to the knife, the boys were found to have a handgun and ammunition when they arrived at school. One of the boys admitted to stealing the gun from his brother, who he said had stolen it from his grandfather.
The boys were reportedly ready to pay $80 in hush money to another student in exchange for keeping the plot a secret.
The trial will take place in juvenile court in Stevens County, Washington.