Why and which kinds of kids in school like to whisper about the quiet kids and laugh about them with others?

I come from London, and believe me they will NEVER grow out of it unless you take action, like i did, by fighting them XD but dont do what i did coz ure gonna face serious consequences this has been going on for 3 years yr 7 to yr 9 and almost yr 10 for another friend. They just dont stop even if thy stoppd talking about you >(