The NICHD Research Program in Reading Development, Disorders and Instruction
Converging Evidence and Findings Relevant to Each Major Research Question: How Do Children Learn to Read?
Evidence and Findings
Reading is not a natural process. In contrast to oral language development, reading does not emerge naturally from interactions with parents and other adults, even in print-rich environments. For most children, reading requires systematic and explicit instruction, although the degree of explicitness, directiveness, intensity and duration of instruction requires developing specific reading components that would vary across children.
Learning to read is a relatively lengthy process that begins very early in children's development and substantially before they enter formal schooling. There is a strong and critical relationship between the amount and quality of early language and literacy interactions and experiences and the acquisition of the linguistic skills necessary for reading. Moreover, frequent language and literacy interactions from birth onward serve to aid in the development of oral vocabulary, an awareness of print and literacy concepts, and an understanding of the goals of reading. Exposure to oral reading and language play (e.g., rhyming) has been found to serve a foundational role in the development of phonemic awareness.
Reading development requires the acquisition of phonemic awareness and other phonological processing skills. Specifically, a necessary foundational skill that beginning readers must master is that the words and syllables that they hear via oral language are composed of small units of sound, termed phonemes.
Becoming aware of the sound structure (phonemes) within syllables and words is made difficult because unlike writing, when communicating orally, the separate sounds composing an utterance cannot be "heard" by the ear due to a process termed co-articulation. Specifically, when producing speech orally, as in saying the word cat, only one sound is heard, not three, as in c/a/t. The vocal apparatus merges the three sounds to permit rapid communication, and it is the brain, not the ear that recovers the sound segments from the acoustic bundle. In essence, to learn to read, the individual must discover that spoken words can be segmented into smaller units of sound, that letters on the page represent these sounds, and that written words have the same number and sequence of sounds heard in a spoken word.
As noted above, the beginning reader must be able to translate print to speech. In an alphabetic language, like English, the individual letters on a page are initially abstract and meaningless optical units. These optical shapes must eventually be linked to sounds - the phonemes discussed above. In essence, the beginning reader must learn the connections between the 26 letters of the alphabet and the approximately 44 English-language phonemes. The understanding that written spellings systematically represent the phonemes of spoken words is termed "the alphabetic principle" and is absolutely necessary for the development of accurate and rapid decoding and word reading skills. The development of sound-symbol relationships is also frequently termed "phonics."
Although the development of phoneme awareness and the alphabetic principle are necessary to learn to read, these skills, in and of themselves, are not sufficient. Specifically, in order for the novice reader to begin to devote more attention and memory capacity to the text that is being read for strong comprehension to occur, phonological and decoding skills must be applied accurately, fluently and automatically. Laborious application of decoding and word recognition skills while reading text reduces attentional and memory resources, thus impeding reading comprehension.
The ability to understand what has been read appears to be based on several factors. Children who comprehend well are able to activate their relevant background knowledge when reading - they can relate what has been read to their own experiences and background knowledge. Strong comprehension abilities are clearly related to oral language comprehension, which like reading comprehension is also critically dependent on the acquisition of a robust oral vocabulary. Individual differences in reading comprehension also vary with the reader's ability to actively summarize, clarify, and predict while reading and the ability to employ syntactical conventions to enhance comprehension.
The development of phoneme awareness, the alphabetic principle, word reading accuracy and fluency, reading vocabulary, and active reading comprehension strategies are all necessary, but not sufficient in and of themselves, to produce robust reading capabilities. These reading elements or components must be exquisitely integrated via informed instruction and practice.
Opportunities to learn to read and to practice the application of reading skills is essential to developing accuracy and fluency and a strong sight word vocabulary. In turn, reading practice serves as a major factor in the continued development of oral vocabulary, particularly as children move past the third grade.
Why Do Some Children and Adults Have Difficulties Learning to Read? Evidence and Findings
Prevalence, Developmental Course, and Psychometric Characteristics
NICHD population-based, epidemiological longitudinal studies indicate that at least 17 percent to 20 percent of the nation's population displays a reading disability. Thus, at least 10 million children, or 1 child in 5 will experience significant difficulties learning to read well enough to utilize reading to learn and for enjoyment. Non-NICHD prevalence studies and assessments (e.g., NAEP) place reading failure at higher levels ranging from 20 percent in some states to 59 percent in others.
While public schools identify approximately four times as many boys as girls as reading disabled, NICHD longitudinal and epidemiological studies show that as many girls as boys have difficulties learning to read.
Reading disabilities typically persist throughout childhood, adolescence, and adulthood. Difficulties learning to read do not reflect a transient developmental lag. NICHD longitudinal studies indicate that of children who are reading disabled in the third grade, 74 percent remain disabled at the end of high school.
Distinguishing between disabled readers with an IQ-reading achievement discrepancy and those without a discrepancy reflects an invalid practice at the beginning stages of reading. Specifically, children with and without a discrepancy do not differ in the information processing skills (phonological and orthographic coding) that are necessary for the accurate and rapid reading of single words. Likewise, genetic and neurophysiological (functional MRI) studies have not indicated differential etiologies for reading disabled children with and without discrepancies. Converging data from several NICHD sites also indicates that the presence and magnitude of IQ-reading achievement discrepancies are not related significantly to a child's response to intervention.
Children with reading disabilities differ from one another and from other good readers along a continuous distribution, and do not aggregate together in a distinct "hump" at the tail of the distribution. Reading disabilities reflect dimensional rather than categorical individual differences.
Environmental, Experiential, and Individual Difference Factors
Children most at-risk for reading failure are those who enter school with limited exposure to the English language and who have little prior understanding of concepts related to phonemic sensitivity, letter knowledge, print awareness, the purposes of reading, and oral language and verbal skills, including vocabulary. Children raised in poverty, youngsters with limited proficiency in English, children with speech and hearing impairments, and children from homes where the parent's or caretaker's reading levels are low are relatively predisposed to difficulties learning to read. Likewise, youngsters with sub-average intellectual capabilities frequently manifest greater difficulties in reading comprehension.