A Tyngsborough high school was evacuated Tuesday after officials discovered a second bomb threat scrawled on a wall in one of the bathrooms, according to police. The threat was discovered at about 1 p.m. in Greater Lowell Technical High School, said Tyngsborough police. Classes resumed after fire and police officials searched the building and determined the threat to be a hoax. Tyngsborough authorities are also investigating a threat reported before classes began Monday morning that was written on the wall of another bathroom at the high school. The student believed to be responsible for the threat reported Monday has been disciplined by the school, according to police.