Similarities and differences between discursive practitioners and scientist-practitioners are discussed in reference to a variety of issues. The scientist-practitioner's approach to generating and evaluating new knowledge is illustrated with two partnerships: (a) between the University of Washington Multidisciplinary Learning Disability Center and a school district (at-risk first graders in the Los Angeles Unified School District) and (b) between the University of Washington Literacy Trek Project and a local school (at-risk second graders in Seattle public schools). Both partnerships involved mostly children who were English language learners. These partnerships also illustrated how Vygotsky's approach to fostering cognitive development through social interaction can be integrated with that of his pupil Luria, who assessed the neuropsychological processes of the individual mind/brain. The most effective instruction for school-age children, who exhibit biological and cultural diversity, takes into account individual and social-cultural variables.