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Environmental Factors Affecting Language Acquisition from Birth – Five:
Implications for Literacy Development and Intervention Efforts
David K. Dickinson
Jill B. Freiberg
Vanderbilt University’s Peabody College
Prepared for the Committee on the Role of Language in School Learning
Draft Version
Language acquisition is one of the miracles of early development and extensive effort has been expended attempting to understand how young children come to acquire such a complex system so quickly. Recently, as scholars have begun to examine the emergence of literacy, it has become clear that there are powerful continuities between early language learning and later academic success and realization that factors such as poverty place children at elevated risk for acquiring language skills associated with later reading. This realization has fueled efforts to intervene with high risk populations. In this report we begin by reviewing evidence of the importance of language to literacy, the association between the birth – five period and later literacy, and then discuss experiences during the birth-to-five years that are associated with enhanced growth and the effectiveness of interventions designed to enhance language learning. Much of the available research focuses on children whose first language is English, but new studies are beginning to explore early language learning of children who are acquiring more than one language. We discuss this work and what is known about interventions designed to facilitate their development.
Language and Early Literacy, Birth - Five
Language-Reading Relationships
By the middle to later elementary school years reading comprehension, the reading skill that matters for long-term academic success, is highly dependent on language abilities. This dependency is at the core of leading theories of reading development, the Simple View (Hoover & Gough, 1990) and the recent Convergent Skills Model of Reading (CSMR) (Vellutino, Tunmer, Jaccard, & Chen, 2007). Both stress the importance of language skill to comprehension and, drawing on findings of many prior studies, the CSMR hypothesizes that there is a shift in the importance of different language abilities as children move from early stages of reading toward becoming skilled readers. Initially, as basic decoding ability is mastered, phonemic awareness, the ability to attend to phonemes, is of major importance because it facilitates the mapping of sound units onto graphemes (Ehri, et al., 2001). As decoding skills are established semantic and syntactic abilities that support language comprehension become of primary importance to predicting reading comprehension. Data collected to test the CSMR are supportive of the theory except that semantic knowledge was found to be equally important at both ages rather than increasing in importance over time. This finding suggests that the conceptual knowledge that is associated with complete understanding of words makes an important contribution to reading even when children are refining basic decoding skills.
Most often studies examining the contribution of language ability to reading ability have used measures of receptive vocabulary to describe language ability and have found that vocabulary is related to reading comprehension (National Reading Panel, 2000). The measures used to assess vocabulary are highly reliable predictors of academic success and therefore are important for gauging children’s access to the language abilities required for academic success in schools in the United States. They are not devised to assess the full range of children’s vocabulary. This is important to bear in mind, especially with respect to vocabulary, because the home language and discourse practices of middle-class well-educated families are likely to be better aligned with language and vocabulary assessed by standardized tools. But vocabulary is only one element of the full language system and assessments of it provide only a partial picture of language ability (Dickinson, McCabe, Anastasopoulos, Peisner-Feinberg, & Poe, 2003). Broader measures of semantic knowledge such as were used in the test of the CSMR, of syntactic knowledge (Nation, Clarke, Marshall, & Durand, 2004; Share & Leikin, 2004), and extended discourse skills such (e.g., narratives, explanations) (Dickinson & Tabors, 2001; O'Neill, Pearce, & Pick, 2004) not only play an important role predicting later literacy, but may be stronger long-term predictors than receptive vocabulary (National Early Literacy Panel, 2008). Advanced reading comprehension also is associated with the ability to become aware of different aspects of language. Phonemic awareness has long been recognized as being of critical importance as children learn to “crack the code” by associating letters with sounds (Stanovich, 1986; Torgesen, Wagner, Rashotte, Burgess, & Hecht, 1997; Wagner & Torgesen, 1987). Skilled reading also has been found to be associated with morphological awareness, an awareness of the units of meaning within words (Deacon & Kirby, 2004; Nation, et al., 2004).
Thus, several decades of research on reading comprehension have found strong associations between reading comprehension and multiple dimensions of language skill and metalinguistic abilities. Questions central to the current report are:
1. Do language abilities in the preschool years predict these later language skills that are associated with reading comprehension?
2. What experiences in the lives of young children predict the rate of development of these language abilities that are related to later reading?
3. Are patterns of association between experience and language abilities similar for children who are learning a new language?
4. What interventions foster enhanced growth of literacy-related language abilities?
Associations Between Early Language and Later Language and Reading
Long-term. There is a growing body of literature linking preschool vocabulary to later reading skill (National Early Literacy Panel, 2008). Storch and Whitehurst (Storch & Whitehurst, 2002) followed 626 children from low-income homes from age 4 through fourth grade and found that preschool language skills had a large indirect effect on reading comprehension in grades 3 and 4. The NICHD Child Care study followed 1,137 children from age 3 to grade 3 and found that age 3 language correlated highly with grade 3 language (r = .73) and had substantial indirect effects of age 3 language on grade 3 reading (NICHD Early Child Care Research Network, 2002). Similarly, Dickinson and Tabors (Dickinson & Tabors, 2001) found that kindergarten vocabulary and word recognition skills, in combination with children’s rate-of-growth on these measures accounted for over two-thirds of the variance in fourth grade reading comprehension (Tabors, Porche, & Ross, 2003).
Measures of language competence other than vocabulary also reveal preschool competencies that predict later language and reading abilities. One study followed low-income children from age 3 to grade 3 and found that age 3 mean length of utterance and diversity of words by children related to kindergarten and grade 3 measures of general language, spelling and reading after controlling for SES and school attended (Walker, Greenwood, Hart, & Carta, 1994). More recently a study of four-year old children who were followed for two years found that age 4 language predicted grade 2 reading comprehension, with grammatical knowledge accounting for more variance than vocabulary (Muter, Hulme, Snowling, & Stevenson, 2004). Detailed long-term studies of language-literacy associations have been conducted by researchers interested in children who experience early language learning problems. Such studies find that early language learning problems portend later literacy challenges (Scarborough, 2001), with the nature of the language problem varying by age. In a recent study of later talkers Rescorla (2009) found that age 2 vocabulary explained 17% of the variance in the age 17 measures of vocabulary, grammar and verbal memory.
Birth-Age Five. Language is a complex system that develops rapidly in the early years. Early language-related processing skills and linguistic knowledge affect later language acquisition and recent evidence suggests that there are reciprocal relationships between early literacy abilities and language. For example, the emergence of phonemic awareness is in part a by-product of early vocabulary development because during the preschool years the size of a child’s vocabulary is associated with improvements in ability to attend to the sounds of language (Munson, Kurtz, & Windsor, 2005; Storkel, 2001, 2003). Given that phonemic awareness is a potent predictor of early reading success, the finding that vocabulary size in preschool fosters its emergence underscores the importance of early language growth to later reading.
The rate at which young children acquire vocabulary is conditioned by other language abilities. For example, children use syntactic cues to help detect the meanings of words and the ability to use syntax to determine meaning varies and children with weaker language skills have more difficulty employing syntactic cues to learn new words (Kemp, Lieven, & Tomasello, 2005). Another indication of how early language bolsters later acquisition is the finding that the rate at which children learn new words is partially conditioned by how many words a child already knows. Children learn new words faster when words are similar to those already in the child’s lexicon (Storkel, 2003). The practical importance of this finding is seen when intervention studies use book reading to build vocabulary knowledge and find that children with stronger vocabularies are more able to learn words that are presented as part of these interventions (Penno, Wilkinson, & Moore, 2002).
Evidence that language is an evolving self-reinforcing system extends into the prelinguistic period. The language comprehension ability and the inclination of 14-month-old toddlers to use gestures to communicate predict their subsequent expressive and receptive vocabulary (Watt, Wetherby, & Shumway, 2006). This evidence of continuity between prelinguistic communication efforts and later language and suggests that early encouragement to communicate may have beneficial effects. Additional evidence of the importance of the earliest phases of language acquisition to later learning comes from the finding that very young children’s capacity to quickly interpret language is related to early vocabulary and language acquisition (Fernald, Perfors, & Marchman, 2006). Early processing ability and related language have long-term effects because language processing speed and receptive vocabulary size at age 25 months are predictive of vocabulary when children are eight years old (Marchman & Fernald, 2008). A meta-analysis of preschool predictors of later reading also found that speed of processing reliably predicts later reading (National Early Literacy Panel, 2008).
In sum, multiple facets of language ability lay the foundation for subsequent language and reading abilities. During the years between birth and five early language competencies facilitate subsequent acquisition suggesting that language is a self-reinforcing system that gains momentum during the preschool years. Evidence is not available that links specific types of preschool language competence to later literacy outcomes, but considerable evidence points to the importance of the rate at which children acquire language. Furthermore, children with a strong early language learning trajectory are at an advantage because, unless a child has a specific language deficiency (Gray, 2005; Johnson & deVilliers, 2009; Nash & Donaldson, 2005), multiple emerging language systems work in concert to facilitate rapid vocabulary acquisition. We now turn to consideration of how environmental factors influence the rate and course of language learning.
Environmental Influences on Language Learning
The finding that early language abilities play an important role in determining later reading and associated academic success raises the question of the extent to which reading is determined by genetic factors as opposed to variability in children’s experiences. One way to address this question is to study identical and fraternal twins. A study of 7,179 twins found that language development and reading ability are largely determined by environmental factors (Harlaar, Hayiou-Thomas, Dale, & Plomin, 2008). Another twin study of early vocabulary and expressive language learning also found that environmental factors accounted for between 54% and 78% of the variation (Van Hulle, Goldsmith, & Lemery, 2004), further highlighting the need to identify environmental factors associated with enhanced language learning.
Some current theories of how children acquire language stress the interplay between biologically determined perceptual and cognitive processing mechanisms, physical and social environmental cues and prior learning (Hirsch-Pasek, Golinkoff, Hennon, & Maguire, 2004; Lidz, Gleitman, & Gleitman, 2004; Waxman, 2004). The Emergentist Convergent Coalition (Golinkoff & Hirsh-Pasek, 2008; Hirsh-Pasek & Michnick Golinkoff, 2008) argues that the child first draws on biologically-driven attention mechanisms, begins to use social cues provided by conversational partners at an early age as well as language-learning hypotheses, and then as acquisition gains momentum, draws on existing lexical and grammatical knowledge. An implication of this theory is that language learning is the result of the orchestration of an impressive panoply of resources that are progressively honed into an efficient language learning mechanism. This view of language acquisition as being progressive determined by children’s agile use of linguistic input implies that, as they near the age of school entrance, children may vary not only in linguistic sophistication but also in their facility with learning language.
Socio-economic status. Socio-economic status is a consistent predictor of variability in the rate of acquisition of vocabulary, complex grammar and skill using language for varying purposes (Hoff, 2006). Variables associated with SES such as income, education, race, ethnicity, and home language covary, making it hard to disentangle their effects. The NICHD Child Care study, a major longitudinal study of children from varied social and economic backgrounds was able to disentangle some of these by virtue of having a very large sample that included collection of a host of measures describing homes, parents and health status. This sample, that included only parents who spoke English, provided information about the impact of home and child care experiences starting at six months on language and on children’s later cognitive and social development. Analysis of the effects of poverty on a broad measure of language development during the preschool years revealed a moderate sized effect of d = .47 (NICHD Early Child Care Research Network, 2002), with poverty being associated with lower scores. This finding is consistent with other studies that have found that persistent poverty has particularly deleterious effects on early development and that the effects of poverty during the preschool years are most likely to have negative effects on children’s development (Britto, Fuligni, & Brooks-Gunn, 2006).
Syntactic development also is related to parental background (Hoff, 2006). Examination of syntactic development between 22 and 42 months of children from various SES backgrounds found that, whereas all children showed roughly similar profiles of development in use of simple syntactic forms, those from the lowest economic backgrounds displayed substantially slower development in use of complex syntax (Vasilyeva, Waterfall, & Huttenlocher, 2008).