Designed by optometrists Garth Christenson, John Griffin, Howard Walton and Graham Erickson
This diagnostic test is normed for grades 2 through 12. It is the gold standard in testing for dyslexia and the definitive and validated test as such, first being published in 1981 with three subsequent editions. The DDT provides evaluation of eidetic (visual) decoding skills of sight-word recognition and phonetic (auditory) word attack skills as well as these categories for encoding (spelling) of words and, also, evaluation of motor skills in writing as regards letter reversals. Testing allows for determination of whether dyslexia is present and, if so, the type and severity of it. Theoretical and validation discussions are included with detailed instructions, with sample cases, for testing administration and interpretation. The results can suggest recommendations for specialized educational therapy if dyslexia is found. If dyslexia is ruled out, recommendations for therapy by other professionals can be suggested when there are reading problems. The DDT comes with Form A and Form B, for test-retest purposes. It comes with an extensive instruction manual, a booklet of plates for word decoding, and recording sheets for decoding results, recording sheets for word encoding results and letter reversal evaluation. Rapid scoring is achieved by use of a laminated reference table.