This is one of a series of reports on the National Longitudinal Study of Mathematical Abilities (NLSMA). This report describes the processes used for deciding what should be measured, when, and how. Work of the SMSG Panel on Tests for collecting tests items, conceptualizing scales, pilot testing, and analyzing pilot test data is reviewed. The development of a model for mathematics achievement is discussed. This model classifies test scales by mathematics content and levels of cognitive behavior. Procedures for the development of the fall and spring batteries for each of the five years of the study are detailed. The selection and development of cognitive processes tests, attitude instruments and role inventories are also included, and the development of the schedule for psychological testing is described. Reports of the First and Second Conferences on Tests and a listing of the NLSMA Scales on Tape are included as appendices. For related documents, see ED 044 277 - ED 044 283, ED 044 310, ED 045 447, and SE 016 670 - SE 016 691. (JH)