For the third time in three weeks, a suburban Detroit school district had to call off classes Friday because someone let the air out of dozens of school bus tires.

Farmington Public Schools officials discovered the flat tires on more than half their district's school buses early Friday.

Officials in the West Bloomfield School District had canceled classes on Dec. 18 after vandals let air out of the tires on about 50 buses there. Waterford School District had do the same two days later.

Waterford Township police Sgt. Todd Hasselbach said Friday that investigators there had identified two teenagers, ages 16 and 17, whom they planned to interview about the December bus vandalism. Police in Orchard Lake, where the West Bloomfield school buses were vandalized, said they had no suspects.

Farmington police said Friday that they were investigating the latest flat-tire incident. The school district has about 12,150 students.

All three districts are in Oakland County, north of Detroit.