Argues that genuine critical thinking requires the recognition of the evolutionary nature of knowledge. Discusses the Perry scheme of nine stages of cognitive development and the Nelson variant of Perry's stages. Discusses teaching methods that are based on this approach and provides suggestions for further research. (CFR)

Examined is the influence and developmental nature of science processes. Results indicated that a one-semester process skills course was effective in developing a basis for science content acquisition. Additional gains can be obtained in an extended curricular sequence. (Author/CW)