Poison Spider School initiated a precautionary lockout Friday morning after Natrona County School District officials learned of an "unspecified threat towards student safety."
The lockout was lifted after investigators began speaking with the juvenile suspected of making the threat.
During a lockout, doors to the schools are locked and there is no outside recess, but school lessons continue.
Authorities are at the school and all students and staff are safe, according to a district statement.
The person who made the threat is not at the school or the surrounding campus, according to the district.
Officials are investigating the threat and immediately contacted law enforcement when they learned of it, the statement says.
In a separate statement, the Natrona County Sheriff's Office said the district contacted it about the threats. Investigators are speaking with a juvenile suspect and do not believe there is an immediate threat to students.
Poison Spider is a K-8 school about 15 minutes west of Casper in rural Natrona County.