Four studies were conducted to examine the manner in which cognitively impulsive and reflective children use private speech to control their behaviors. The first study was a naturalistic observation of a group of impulsive (N=8) and reflective (N=8) nursery school children, identified by the Matching Familiar Figures Test. The Impulsive and reflective children differed significantly in the amount and style of verbalizations and in the content and incidence of private or egocentric speech. In a second study the relationship between reflectivity/impulsivity and verbal control of motor behavior was examined with 30 kindergarten children. Under covert self-instructions, impulsive children evidenced significantly less verbal control of inhibitory motor behavior and a greater magnitude of errors than reflective children. The efficacy of a cognitive self-instructional (SI) training procedure in altering the behavior of "impulsive" school children was examined in two studies. Study III employed an individual training procedure requiring the impulsive child to talk to himself. Results indicated that the SI group (N=5) improved significantly on three measures and retained the improvement after one month. Study IV examined the efficacy of the components of the cognitive treatment procedure in altering the impulsive child's performance on Kagan's measure of cognitive impulsivity. Cognitive modeling slowed down the response time for initial selection, but only with the addition of self-instructional training was there a significant decrease in errors. (Author/KM)