(bm) The school district administrator or any principal or teacher designated by the school district administrator shall suspend a pupil under par. (b) if the school district administrator, principal or teacher determines that the pupil, while at school or while under the supervision of a school authority, possessed a firearm, as defined in 18 USC 921 (a) (3). This paragraph does not apply to the possession of a firearm while legally hunting in a school forest if allowed under s. 120.13 (38). [...] 2m. The school board shall commence proceedings under subd. 3. and expel a pupil from school for not less than one year whenever it finds that the pupil, while at school or while under the supervision of a school authority, possessed a firearm, as defined in 18 USC 921 (a) (3). Annually, the school board shall report to the department the information specified under 20 USC 8921 (d) (1) and (2). This subdivision does not apply to the possession of a firearm while legally hunting in a school forest if allowed under s. 120.13 (38).