Not necessarily. My company’s softball league pulls from all levels of employee, from factory workers to upper management. My husband’s soccer league is extremely mixed, although the teams are somewhat more clustered by SES.
My husband’s closest friends are the guys he plays with in a men’s league. The great thing about getting to know these guys through soccer is that initially no one knows or cares who does what for a living or where/if they went to college. All they care about is that they play well, and since a lot of the best players in the league are immigrants, not being a white guy from the suburbs is if anything a plus in their eyes. They all wear the same thing-shorts and t-shirts to practice, uniforms to games, and since most of the socializing happens around these events they got to know each other without many of the most obvious trappings of class. Every once in a while something happens, such as a crisis in someone’s life, and you learn who lays bricks for a living, who’s a neurosurgeon or attorney, who’s former Mossad, who’s been out of work for 5 years.
Upthread someone said something about socializing outside your SEC not just being about socializing with your Mexican gardener and it made me laugh because our Guatemalan gardener is a friend, met through soccer. We socialize with the whole extended family and his nephew is one of my husband’s closest friends.
That said, I agree that most people socialize primarily within their own SEC. I know most of the people I interact with on a daily basis are similar to me in educational background and income, with some but not much variation up and down the SES scale. A lot of that is a function of living in the suburbs. When I lived in the city my neighbors were much more varied in terms of income, race, and social background.