Decodability Tool

For testing the decodability of pupil-read stories
by Dr. Patrick Groff
NRRF Board Member & Senior Advisor
and Ann Edwards, M.A., Ed.

Dr. Patrick Groff, Professor of Education Emeritus at San Diego State University, has published over 325 books, monographs, and journal articles, and is a nationally known expert in the field of reading instruction.

Ann Edwards is the NRRF 2004 Teacher of the Year.

Purpose of this Decodability Tool
Application of this Decodability Tool will determine if stories in reading programs are “decodable texts.” Implementation of the steps outlined below will determine the percentage of decodable words in any text.

What is “Decodable Text”?
A story text is “decodable” only if ALL the speech sound-letter correspondences in ALL the words in that text have been taught prior to the introduction of the text to the student. This means that reading programs with “decodable texts” have systematically and explicitly taught all the speech sound-letter correspondences necessary to decode (read) words in them BEFORE the child encounters these words in a text.

For example, to properly read the word cat, the child must have been taught each of the three speech sound-letter correspondences: c = /k/; a = /a/; and t = /t/. In laundry, there are 6 speech sounds and combinations that the child must be prepared to decode. For laundry to become a decodable word, the child would have to have had instruction in all 6 speech sound-letter combinations: l = /l/; au = /o/; n = /n/ ; d = /d/; r = /r/; and y = //. Having had instruction in fewer than six speech sound-letter correspondences would make laundry “nondecodable.”

Special Background Information for California Residents
The legislature of the state of California, concerned by the dismal reading test scores of students in its public schools caused by the widespread use of “Whole Language” practices, has passed laws to bring “systematic, explicit phonics instruction” back into the classrooms. To meet the requirements established by the new laws, text presented to all students must be “decodable.” This new emphasis on how reading is to be taught in California, has textbook publishers scrambling to make their programs “fit” the criteria recommended by the State Board of Education. Nonetheless there are many current publishers of reading materials who claim to have “systematic, explicit phonics instruction” in their programs. However, one must be careful NOT to allow that these programs represent “systematic, explicit phonics” instruction. For a program to qualify as using “systematic, explicit phonics instruction,” a major requirement is that its stories are “decodable texts.”


It is important that the different people doing the study apply the same phonetic “rules” in order to count the same words as “decodable.” That’s why it’s helpful to be available to each other during the work time in order to clarify confusing areas:

  1. Persons wanting to do this type of analysis must have a working knowledge of speech sound-letter correspondences that make up the body of knowledge termed “phonics.” It’s best to have two or more people working independently of each other during the analysis. They must periodically clarify results they obtain with each other. Afterwards, they must cross check results to eliminate errors. It is important to for analysis cross check both separately, and together.
  2. Decide on the grade level to be studied (usually beginning kindergarten, first or second). Locate the publisher’s materials for that grade, including all Teacher’s Editions and student texts. A catalog from the publisher usually shows every title.
  3. Locate the reading materials to be analyzed at the district office of the local school district or at the regional educational resource center for the county or state. Call ahead to determine if the materials are available for review.
  4. Allow ample time in order to do the analysis. DO NOT RUSH.
  5. Do the analysis on approximately the first 10-15 stories at the beginning of a particular grade.
  6. Have available a notepad or laptop computer, a pencil, a highlighter, and a calculator.
  7. Find story #1 in the student text and make an alphabetical list of all the words in that story.
  8. Look at the Teacher’s Manual and list the speech sound-letter correspondences taught for that story. The speech sound-letter correspondences for each story usually appear in the Teacher’s Edition under the headings “phonics” or “phonemic awareness.”
  9. Using an alphabetical list of words, underline, circle or highlight each speech sound-letter correspondence taught whenever it appears in the words for that story. For example, if the teacher’s guide introduces 5 speech sound-letter correspondences for story #1, one must look at every word in that story and mark where those 5 speech sound-letter correspondences occur.
  10. In subsequent stories, credit should be given for speech sound-letter correspondences taught all the way back to lesson 1. Thus, if one is in lesson 8, credit is given to all speech sound-letter correspondences taught back through lessons 1-7. The list of speech sound-letter correspondences taught grows as one accumulates them from story to story.
  11. Total the number of decodable words in each story. Remember, if any speech sound-letter correspondences in a word have not been taught previously, that word is not decodable. A child may have been taught /m/=m and “silent e,” but knowing those 2 speech sound-letter correspondences does not mean “mouse” is decodable because the /ou/ and /s/ speech sound-letter correspondences have not been taught.
  12. Total the number of words in the story.
  13. Divide the number of decodable words by the total number of words in the story.
  14. The result is the percentage of decodable words in that story.

For example, if a story contains 34 words and 2 of those words have had all of their speech sound-letter correspondences taught, divide 2 by 34 for 5.9%. The percentage of “decodable” words is 5.9%. That is, only 5.9% of speech sound-letter correspondences in those 34 words were taught before the child encountered them in print.

Subtracting 5.9% from 100%, the percentage of words that are “nondecodable” is 94.1%. This means that 94.1% of the words for that particular story did not have their speech sound-letter correspondences taught prior to being introduced to the student. That is, for 94.1% of the words children were not prepared ahead of time to sound out (decode) the words. They are not decodable words.

It becomes clear after a few stories if a program teaches the speech sound-letter correspondences of words prior to the lesson, or whether the program presents words that are not decodable. The former is “systematic, explicit phonics” instruction. The latter is “whole language.” Teaching the former is in compliance with the California laws. The latter is not.


  • The publisher may teach rhyming words, word families, plurals, endings, etc., but these are not counted as speech sound-letter correspondences taught. Anything that was not taught as an individual speech sound-letter correspondence is left out.
  • Count “blends” (e.g., sl, br) only if both speech sound-letter correspondences have been taught individually.