RICHFIELD, Idaho — Officials with the Blaine County School District say its transportation director has resigned following a school bus crash that rolled over and injured more than a dozen students in April.

Superintendent Dr. GwenCarol Holmes said Thursday Rex Squires resigned after being presented with findings of an investigation that found procedural violations. Holmes did not detail what violations were discovered.

Assistant superintendent John Blackman will serve as the acting transportation director while the district searches for a replacement.

On April 18, junior high students from Carey School were on their way to a track meet in Gooding when their bus crashed about 125 miles (201 kilometers) southeast of Boise on U.S. Highway 26. Officials say 67-year-old Richard Mecham drove off the right shoulder, overcorrected and rolled the 2011 school bus.

Twelve students were hospitalized. All were released the next day.