An estimated 15% of Americans participated in school groups in 2009 and 18% participated in religious organizations.  At roughly that same time, average household income was $69,000.  Rates of participation in different types of community groups and average household incomes do not appear to be very highly correlated across states or large metropolitan areas.  Thus, people participate in groups regardless of their incomes and perhaps base their participation decisions in these groups on the characteristics of their family and neighbourhood.

Civic Participation And Household Incomes

Source: Jonathan Schwabish