The Rangemaster is a teacher at Rommelwood Military School.
He gave a fearsome-looking grenade launcher to Bart, because he concluded that Bart can use small arms, according to attending public school. Bart did very well at shooting and the rangemaster praised him.
However, Lisa had many problems with shooting. She somehow got her rifle stuck on "auto-fire" and could not stop it. The rangemaster helped her and gave to her a whistle. He told her that if she blows on it, he will come help her.