The thesis that Mexican Americans share a monolithic, "pathological" subculture that causes difficulties Mexican American children may have in adapting to Anglo society is challenged, using data from studies of Mexican American families and youth. Origin of the theory that all Mexican Americans share a negative subculture is detailed, and influence on educational policies noted. Findings from Texas A & M studies (15 years of research on Mexican American youth and a 1978 study of 172 lower class Mexican American households in Cameron and Brooks counties, South Texas) indicate dramatic variability among Mexican Americans in family structure/practices, language usage patterns, ethnic label preferences, life goals/aspirations, desires for community improvement, and religious participation/practices. A synthesis of findings from the South Texas study concludes that Mexican Americans show marked value diversity (sometimes polarized into opposing valuation positions) concerning family and kin, gender roles, religiosity, and social conservatism vs. liberalism. The clearest case of value consistency was an almost universal desire for structural assimilation with Anglos across a wide variety of social contexts, although many would also wish to maintain distinctive ethnic cultural traits such as Spanish-English bilingualism. Metro-nonmetro differences in value diversity are judged to be of minor significance. (MH)