Book excerpt: "The reliability and validity of information obtained from any psychological test is dependent on the scope and psychometric attributes of the instrument used. As in all areas of science, what psychologists discover depends on the quality of the instruments used and the information they provide as well as skillful interpretation of the test results. Better conceptualized instruments yield more accurate and informative data than do weaker instruments. Instruments that uncover more useful information about the individual being examined are more valid and ultimately better inform both researchers and clinicians. The tools school psychologists choose for diagnostic decision making substantially influence the reliability and validity of the information they obtain and the decisions they make. Simply put, the better the tool is, the more valid and reliable the decisions; the more useful the information obtained is, the better the services provided. In this chapter, some important issues regarding quality and effectiveness of the tools used in school psychology are discussed"--Book. (PsycINFO Database Record (c) 2013 APA, all rights reserved).