Lockport, NY- For the second time this month, a western New York school is closed after more than two dozen students become ill.

North Park Middle School in Lockport, Niagara County was evacuated yesterday after about 30 students and teachers were apparently sickened by carbon monoxide.

Superintendent Bruce Fraser says tests showed slightly elevated levels of carbon monoxide in the blood of those taken to the hospital after complaining of headaches and nausea. The sickened students and staff were treated and released from the hospital.

Fraser says officials believe the carbon monoxide came from a boiler that provides heat for the school building.

All 645 pupils were sent to other schools in the district northeast of Buffalo.

More tests are planned today before school officials decide whether to reopen the middle school. The district begins its Christmas break on Friday.

The high school in the neighboring town of Pendleton was closed for three days last week when 31 students became sick while rehearsing for a concert. Officials are still trying to determine what caused the illnesses.