The role of the classroom teacher as a diagnostician is described. Since the purpose of reading diagnosis is to ascertain the probable potential of each student and to determine what his instructional needs are and where to begin instruction, extensive individual testing is neither possible nor recommended for the classroom teacher. However, reading expectancy, self concept, and motivation can be determined from teacher observation and school record analysis. Also, the best instrument available to the classroom teacher for obtaining information about groups of children is the standardized test. The uses, advantages, and disadvantages of a group standardized test for screening and grouping pupils are discussed. Some guidelines for analyzing and comparing subtest scores to obtain diagnostic information and for interpreting test behavior are given. (CM)