South Gate High School is one of four schools hit. Tubas and sousaphones, $30,000 worth, were taken from the band room.
Eight sousaphones were stolen from Centennial High School, and tubas were also seized at Fremont and Huntington Park high schools.
There have been no arrests. Teachers think the thefts could be connected to the popularity of Mexican banda music, featuring tubas.
Students at South Gate now have to share two clunkers.
"The old ones that we're currently using, they have tuning issues," said Erik Camberos, a junior at South Gate High School.
The students said they just want their instruments back. They're now taking precautions and leaving the instruments they still have at home.