This study examined the possible sources of variability in sign language mastery in two deaf children of hearing parents. The study considered the interaction of environmental and innate factors within the framework of the "Nativization" hypothesis, which suggests that all language learners initially construct a linguistic system which is somewhat unique and then gradually adapt to the environmental target language unless the input is inaccessible or inconsistent, in which case the learner creates grammatical constructions that further depart from the external norm. The ethnographic study focused on the sign language structure of the two children, ages 8 and 9, and the sign language used by their mothers. The study found that, when presented with a variety of input, deaf children of hearing parents show a preference for American Sign Language (ASL) as a target language. Hearing parents who are supportive of their children's involvement with deaf people and communicate in a way which approximates ASL appear to provide optimally useful environmental input. The child who was more advanced at a younger age in his grammatical development subsequently developed a greater range of stylistic variation in his signing. Appendices contain a glossary, hypothetical scenarios which typify four home environments for deaf children acquiring language, and guidelines for ethnographic data collection. (Over 100 references are provided.) (JDD)