Research on measurement of intelligence has a very long history. Efforts have been made to evaluate other areas of functioning. In some cases the development of assessment instruments has been driven by commercial motives rather than the. Instrument development has occurred at a very rapid rate, often at the expense of careful and deliberate thought about. There has been a significant proliferation of psycho-educational instruments in the past 30 years. New instrumentation is being developed continually at an accelerating rate. Questions arise about the degree to of technical precision. Many instruments on the market do not give adequate attention to sound measurement practices. Development and articulation of measurement concepts regarding the reference used for data interpretation represents. This refers to what standards or comparisons are used for a child"s performance. Most prominent in this work is the distinction between norm- and criterion-referenced evaluation.