It is entirely natural for children to “clown around” in a boring setting, and their lack of interest / trouble focusing reflects a societal (and school) failure to make school engaging and give them the appropriate challenges and direct feedback to keep their attention. Many of the greatest human breakthroughs were made by people who were squirmy and distractible as children, who had difficulty with the formal school curriculum, or who were ostracized by their classmates for one reason or another.
Every child deserves attention from good teachers. Good teachers with enough resources can provide a significant benefit to these students and integrate them into a smoothly functioning classroom. Assigning troublesome students to weak or unsympathetic teachers is a tremendous “waste” of human talent.