North Wasco County School District 21 reports a Chenowith Elementary School student set off a travel-sized canister of pepper spray on one of its school buses Tuesday afternoon as it was loading students to return home.  In a letter to parents posted on the D-21 Facebook page, the district says all students were evacuated from the bus, assessed, and brought to the cafeteria for observation.  A new bus was brought in to take students home.  The district says families of affected students were contacted.