BOISE, Idaho—A sixth-grade girl brought a gun to her Idaho middle school, shot and wounded two students and a custodian and then was disarmed by a teacher Thursday, authorities said. The three victims were shot in their limbs and expected to survive, officials said at a news conference. Jefferson County Sheriff Steve Anderson says the girl pulled a handgun from her backpack and fired multiple rounds inside and outside Rigby Middle School in the small city of Rigby, about 95 miles southwest of Yellowstone National Park. A female teacher disarmed the girl and held her until law enforcement arrived and took her into custody, authorities said, without giving other details. Authorities say they’re investigating the motive for the attack and where the girl got the gun. “We don’t have a lot of details at this time of ‘why’—that is being investigated,” Anderson said. “We’re following all leads.” The girl is …