This critique of James Gallagher's Topic Classification System (TCS), a tool of categorizing teacher-pupil classroom interaction, suggests revision of the system asking for more complete analysis of the data obtained with it, but recommends its use in future investigations especially in view of its organization and the "unique elements" it contains. Four questions are posed for consideration by the potential user of any category system: 1) Are the coding instructions and procedures sufficiently clear so that the coding teams will not have to make up additional coding instructions? 2) Are the coding instructions and procedures sufficiently clear so that the results of independent investigations using the category system can be compared? 3) Are there variables in the category system which are related to pupil outcomes measures? 4) What variables of interest are included or omitted from the category system? The TCS and accompanying descriptive reports are analyzed from strengths and weaknesses in light of each of the four questions. Included is discussion of coding procedures, cognitive variables not included; unique elements in the TCS (inclusion of content as part of the coding of topics, three cognitive dimensions. and the style categories); the three-dimensional classification (instructional intent, level of conceptualization, and style); the TCS and other category systems; and Gallagher's use of the TCS. A 104-item bibliography is included. (JS)