Take a picture book or a chapter from a novel and assign each character's dialogue to a different student. No memorization, no costumes, no stage — just kids reading their lines aloud from the book while the narrator reads the non-dialogue portions.

This is the single most effective activity for building reading fluency in a classroom setting. Students practice their lines (repeated reading = fluency), perform for an audience (motivation), and hear the text interpreted through multiple voices (comprehension). It also gives reluctant readers a reason to practice — they don't want to mess up their lines in front of the class.