The development of children's language skills was studied in an experimental research project involving programmed versus incidental instruction in a prekindergarten program. It was hypothesized that children who attended a prekindergarten with programed instruction would score significantly higher on language skills tests than would a comparable group of children receiving incidental instruction. Subjects for the study were 43 4-year-old children, randomly assigned to one of three prekindergarten groups, two experimental and one control. All the children were from white, English-speaking, middle-class families with an unusually high parental educational level. The curriculum for the experimental groups was based on behavioral objectives implemented through daily lesson plans. The control group curriculum was based, at the start, on the traditional nursery school approach, with behavioral goals not explicitly defined in any curriculum area. Although post-testing results showed no apparent significant difference in language skills between the experimental and control groups, the negative findings were attributed to intervening factors: (1) the control group program had been altered, contrary to the original plan, offering the control children language opportunities quite similar to those of the experimental groups; (2) teachers in the experimental groups were not sufficiently familiar with techniques of programmed teaching; and (3) the programmed curriculum manuals had been designed for disadvantaged children. Results showed that specific and well-defined behavior management and direct teaching techniques, with a curriculum based on explicit behavioral objectives, are not in themselves sufficient to effect a significant change in either language skills scores or intelligence quotients of 4- and 5-year-old children. The study also showed that a language development program designed for disadvantaged children is not appropriate for middle class children with college-educated parents. (Author/BF)