This article describes a procedure to aid in the clinical appraisal of child speech. The approach, based on the work by Dinnsen, Chin, Elbert, and Powell (1990; Some constraints on functionally disordered phonologies: Phonetic inventories and phonotactics. "Journal of Speech and Hearing Research", 33, 28-37), uses a railway idiom to track gains in the complexity of speech sound production. A clinical case study is reviewed to illustrate application of the procedure. The procedure is intended to facilitate application of an evidence-based procedure to the clinical management of developmental speech sound disorders. (Contains 2 figures, 1 table and 3 notes.)