‘The act of discovering or identifying the exact cause of an illness or problem’ (Oxford Learner’s Dictionaries).
Diagnosis is one particular use or purpose of assessment information. It aims to identify particular strengths and weaknesses a learner may have in one or more areas of their functioning. Diagnosis often implies the collection and interpretation of information from a medical perspective, although educational ‘diagnosis’ also occurs. Diagnosis is often one aspect of assessment processes linked to initial identification of special educational needs.