Despite current research evidence connecting family involvement to students' academic learning, non-mainstream families' funds of knowledge are insufficiently valued as relevant to public schools' curricula and academic genres, a practice that limits diverse families' inclusion as equal partners in their children's education. This two-year-long ethnography (2005-2007), grounded in sociocultural and sociohistorical theories, investigated the struggles and possibilities that two elementary teachers and their students' non-mainstream families faced while trying to reach common understandings about working collaboratively to develop home-classroom partnerships at a time of a national educational reform under the politics of high stakes accountability of the NCLB Law of 2001 and a state local policy of English-only education in Western Massachusetts. Focusing on a third grade teacher and her English Language Learners (ELL) Latino students and on a regular kindergarten teacher with half of the students of Latino origin, the study explored the evolution of participants' assumptions about non-mainstream students and their families, the participants' co-construction of social and literacy practices, and the dialogical practices conducive to partnerships for fostering home-school partnerships and improving diverse students' literacy development. Findings suggest that: (1) some specific social and literacy practices co-constructed through dialogical interactions between urban school teachers and Latino families positively influenced home-classroom partnerships that worked for nonmainstream families; and (2) the participant teachers' critical reflections on their own assumptions and ideologies brought them new understandings about Latino families' funds of knowledge and child socialization practices, helping them to know the whole child and to better provide academic support for ELL students. Implications for practitioners point at the importance of gaining an in-depth understanding of building relationships with non-mainstream families in urban schools to implement home-school partnerships that work for all families. Implications for state agencies, stakeholders, and administrators are: (1) a need to redefine the field of family involvement for a comprehensive action plan for involving non-mainstream families as equal partners in their children's education; and (2) the need for serious commitment towards supporting urban teachers by allocating time and funds for professional development.