Structural integrity of a measure is defined in terms of its replicability, constancy, invariance, and stability. Work completed in the development and validation of the Self Observation Scales (SOS) Primary Level (Stenner and Katzenmeyer, 1973) serves to illustrate one method of establishing structural integrity. The name of each scale of the SOS is a construct: an abbreviated thesis about the nature of the underlying variable which determines the configuration of indicants (questions) comprising the scale. SOS constructs (self acceptance, social maturity, school affiliation, and self security) are analyzed for different student groups. Traditional psychometrics assumes that the same questions measure the same underlying variables in all respondents; the validity of interperson and intergroup comparisons rests on this assumption. However, ample evidence suggests that this assumption is frequently in error. Procedures outlined in this paper provide a method for assessing the validity of this assumption, and a basis for developing reliable and valid instruments. (Author/MV)