The SAND school in Hartford was evacuated on Friday after a possible threat, but students were allowed back in after police determined it was safe.
Police said the possible threat was a vague, unsubstantiated social media threat and no children were in danger. Police and school security staff swept the building.
The power was also out and Eversource, electricians and facilities staff were investigating the problem.
Power was also out at Global Communications Academy and Thirman Milner School, but the power has been restored at these two schools.