This paper advocates that assessments of children's educability should utilize strategies based on a paradigm of plasticity of intellect within a wide range of hereditary limits rather than on a straightforward heritability paradigm. The relationship between science and values is discussed and the role of each in the creation of Project Head Start is delineated briefly. The failure of Head Start to achieve its middle class achievement goals for poverty children is portrayed as the basis for a conceptual backlash which has brought hereditary theories of intelligence back into contention. The concept of heritability (that proportion of the variance in any measurable phenotypic characteristic attributable to the variation of genotypes within the population) is examined in detail and its lack of relevance to the concept of educability is argued. The concept of range of reaction (that variation in any observable, measurable phenotypic characteristic that a given genotype can produce in response to variation in the environment or life experience) is discussed in detail. The major portion of the paper presents data illustrative of a research strategy suggested by the concept of the range of reaction. Data reported include empirical and anecdotal data on the language, achievement and personality of children from an orphanage in Tehran and a brief review of related cross-cultural and adoption studies. (JMB)