During my childhood my family moved several times, including a stint overseas, which resulted in my attending six different schools during my pre-college years. That means I averaged a maximum of two years at any given district before we up and moved again.
Parents don't usually think about these type of things during a relocation, but any school-age kid who’s experienced such nomadic maneuvers, has likely experienced the corresponding phenomenon of bullies.
While not unique to me (my sisters and brother didn’t have an easy go of it I'm sure), it seemed that I was getting in fights at every new school as the resident bully had to assert his “alpha-ness” against the new kid.

