Richwoods High School was on soft lockdown during second hour classes Friday morning.
Ameren Illinois had planned to shut off power to the building to make repairs necessary after an earlier power outage. However, District 150 officials say the utility did not have to shut down the power, the lockdown was lifted and classes resumed as normal.
The initial power outage occurred before students started arriving for the 7:30 a.m. start of the school day. District 150 allowed students to sign out and return home, but urged students to come back to school when power was restored around 8:00 a.m.
Students who properly signed out with parents' permission before power was restored, but were unable to return to school, will get an excused absence.
D150 officials say around 50 students were signed out and most of them returned to school.