This study concerns an analysis of articulatory substitutions of 801 students using markedness theory and a distinctive feature model (Singh & Singh, 1976). The 556 male and 245 female students ranged in age from 3--7 years and were diagnosed as evidencing an articulatory disorder or a linguistic delay. Significantly more feature substitutions moved from marked to unmarked values than from unmarked to marked values (p less than .05, binomial distribution). The study proposed a hierarchy of distinctive features in terms of markedness rather than in terms of features per se. The applications of articulatory and acoustic data to phonological theory and the implications of the findings to speech treatment are discussed.