Kevin Burns, director of public affairs for Mayo Clinic Health System Springfield, said the 30 students were treated for nausea and headaches, the (New Ulm) Journal reported. All but one had been released by early evening, with the one child kept for observation, Burns said.
Springfield Fire Chief Charlie Baumann said a thorough check of the school building found no carbon monoxide as of 3:30 p.m. CST. He said officials planned to recheck the school again Friday morning before students and staff arrive.
Baumann said classes would likely start 2 hours late.
Springfield Police Chief John Nicholson told the newspaper the children became sick while rehearsing for a music program at the Springfield Public School auditorium. The children were fifth- and sixth-graders, he said.