Each child left the school with a stranger, unaware of a videotaping of the test. Tests of language development, self-esteem, and knowledge of prevention and safety concepts were given before and after subjects participated in the Children Need to Know Personal Safety Program. A primary prevention program based on age-appropriate, experiential, and interactive instruction was documented. Higher self-esteem before instruction and higher knowledge/attitude scores after instruction were found to predicate a reduction in vulnerability. The study concludes that traditional use of cognitive questions which elicit written or verbal responses about safety are sometimes misleading. 1 table and 13 references. (Author abstract modified)