The Boy Scouts of America relies on a "Chartering Organization" model for each of it's units. A Chartering Organization could be a business, a civic group like the VFW, or an educational institution, like the PTA of a local school. However, a large number of these chartering organizations (Almost 70%) are religious institutions.
The BSA has some statistics here about what kind of groups charter units.
Each chartering organization agrees to serve families and youth via their scouting program.
Some organization focus primarily on serving the current members of their group. Examples might include the LDS Church, who uses the Cub Scout / Boy Scout Programs as an integral part of their church's youth program, or a Private School that operates a Pack that is open only to boys who attend that school.
The majority of units serve the larger community, meaning that boys from families outside the organization are welcome to join. Particularly for religious chartering organizations this can lead to some confusion where religious advancements are concerned, as you may frequently have a situation where a unit meeting at a United Methodist church has boys from families who attend Catholic, Baptist, or even Muslim or Buddhist houses of worship. I'll get into this in more detail in later posts.
The Chartering Organization agrees to
In my personal experience, I find that a large number of Chartering Organizations primarily focus on providing meeting facilities, and assume the rest of it will be taken care of by parents inside the unit. This often leads to a unit that is poorly supported.