The purpose of a diagnostic test in education is to assess the current state of a student's progress or ability in a particular area. Some diagnostic tests determine if a student qualifies for special education services on the basis of everything from dyslexia to speech delays or even attention deficit disorder while others indicate specific competencies on the scope and sequence for a course in which students have either demonstrated mastery or need remediation.
Another term for a diagnostic test in education is a formative assessment or evaluation. The use of these instruments in education is still relatively recent as the terms only entered pedagogical parlance in 1967. The purpose of formative assessments in the general education classroom is to determine whether a particular curriculum is effective as well as whether the teaching practices of individual educators are effective. The various factors that contribute to student success on assessments make it problematic to assign either failure or success solely to the efforts of the classroom teacher, which means that there is a tension between administration and educators (as well as between politicians and the educational establishment) about the value of diagnostic assessment and whether curriculum should prepare students specifically for their end-of-year diagnostic assessments.