I believe that LE at a press conference actually clarified that.
Terri called the school, and then when the school couldn't locate Kyron and realized he was missing, they called 911:
When Kyron didn't come home on the bus that Friday afternoon, his parents called the school, which in turn called 911, launching what Gates said could be the largest search operation in Oregon history.
LINK
3:46 p.m. reported to be from Skyline elementary staff, law enforcement records and Desiree:
School secretary Susan Hall places 911 call and reports Kyron missing to authorities. Susan then calls Desiree and informs her of Kyrons missing status. Desiree speaks with Terri immediately afterward on Terris cell phone. Desiree states she was immediately concerned because statements Terri made during that phone call didnt make sense.
LINK