The placement and diagnostic tests used in instructional systems designed to be adaptive to the individual learner's characteristics are examined. The necessity of pretesting students before instruction is questioned. According to the author, both the necessity for and the content of the Individually Prescribed Instruction (IPI) type of pretest should be more carefully examined. While the diagnosis of errors is viewed positively, the need to prescribe specific instruction for every type of error is doubted. The importance of analyzing the psychological structure of a specifc course, thereby determining the sequence of tasks necessary in order to facilitate later learning, is stressed. Examples of various types of placement and prescriptive procedures, including Individually Prescribed Instruction and adaptive testing are presented. (Author/MV)