In simple terms diagnostic testing consists of asking the learner to attempt certain tasks, so that the teacher can gain insights into his difficulties by observing his performance on them. Teachers will differ in the procedures they use to obtain this information. Some will use an oral reading setting as detailed by Clay (1972) or Goodman and Burke (1972). Types of errors will be noted and appropriate programmes for remediation devised. Some will use an informal prose inventory of the type advocated by Holdaway (1972) while others will use a published standardized test like the Neale Analysis of Reading Ability. The purpose of this article is to provide teachers with information which may assist them in reaching decisions concerning the use of diagnostic tests of reading.