HILLSBORO, Ore. - Six sixth-graders were injured Friday when the bleachers they were sitting on collapsed while they posed for a class photo.

School officials said about 50 children were standing on the bleachers at West Union Elementary School when the incident took place.

The structure is reportedly a standard-style metal bleacher with seats three to four feet off the ground. Friday afternoon, investigators said that supporting cross-beams under the seats had been removed.

Six students in all suffered minor injuries and three were taken to the hospital. Parents of the other injured children were left to decide if they required further medical attention.

The other students returned to classes and the school day resumed. One parent told KATU News she felt the school handled the incident properly.

Since the bleachers were tampered with, investigators said the children would be classified as victims in a criminal case and an investigation would be started to find who removed the support pieces.

Crime scene investigators dusted the structure for fingerprints and looked for other evidence.

The investigation is continuing.