Second language acquisition is learning of a nonnative language (i.e., second language) sometime after learning a native language (i.e., first language) has begun. A central characteristic defining second language acquisition is that it occurs in the context in which that language is spoken. For example, native Spanish speakers learning English in the United States or native German speakers learning Japanese in Japan are considered second language learners. However, learning a second language may or may not take place in the context of classroom instruction.


Second language acquisition is different from learning a foreign language. Second language acquisition of a nonnative language occurs in an environment in which the nonnative speaker has easy access to speakers of the language being learned. In contrast, foreign language learning refers to the learning of a nonnative language in the environment of one's native language. For example, a native English speaker learning French in the United States would be learning a foreign language (Gass & Selinker, 2001).

Understanding second language acquisition requires understanding the difference between learning a first language and a second language. First language develops without formal instruction by children being constantly exposed to language rich environments over the course of many years. The richness of the language environments in which children learn—the amount of language they are exposed to and type of language they are exposed to— influences how thoroughly children learn their native language. Also, as children learn their native language what they learn influences how well and how rapidly native language learning will occur (Hart & Risley, 1995). In contrast, learning a second language usually depends heavily on learning experiences in more constricted environments associated with the classroom or some other formal setting. In these settings, a major goal frequently is to formally teach children the elements of language that are learned much more informally in their native language. Consequently, assumptions regarding teaching and learning a second language are very different from assumptions about children learning their native language.


Acquiring any language means learning five primary linguistic elements: phonology, syntax, morphology, semantics, and pragmatics. Phonology is the knowledge of the sound system in a language. It involves knowing what happens in words in fast speech as opposed to more carefully articulated speech. For example in the sentence: “I'm going to ride my bike”, it is plausible that a second language learner would believe the correct pronunciation would be: “I'm goin to RIDEMYBIKE” (i.e., the learner does not articulate all of the phonemes in words and runs words together because she does not hear the words and sounds distinctly).

Phonology. Phonology includes knowing all of the sounds that are included in a language and knowing how the sounds are combined. For example, the English letter combinations sc, sp, and st, do not exist in Spanish at the beginning of words. Thus, to pronounce these letter combinations, native Spanish speakers learning English tend to add an /e/ sound to the beginning of these letter combinations (e.g. /esc/, /esp/, as in eschool, especial) because in Spanish words with sc, sp, and st combinations begin with an /e/ sound (e.g. “escuela”, “especial”).

Syntax. Syntax is grammar, the rules that govern word order in sentences. Knowing the grammatical rules allows the speaker to produce an infinite set of sentences that can be easily understood by any individual proficient in that language. For example, the sentence: “The green turtle ran across the street to look for her friend the duck,” can be understood by proficient native English speakers even though it is unlikely that the individual has encountered this particular sentence before (Gass & Selinker, 2001).

Morphology. Morphology is the study of word formation. Morphemes represent the minimal unit of meaning in words. For example, the word fitness is made up of two morphemes: fit and ness. Ness is considered a bound morpheme because it can never be a word by itself, while fit is defined as a free morpheme because it is a word in and of itself like the words man, woman, and moon. Words can be created by adding morphemes, as in entangle: dis+entangle, dis+entangl+ing. The ways words are used in sentences also follow accepted patterns. For example, English speakers say, “Mt. Everest is a high mountain,” but not “The Empire State Building is a high building.” (They would say, “The Empire State Building is a tall building.”) Sometimes the reason certain word combinations are appropriate is clear, while at other times the combination appears to be quite arbitrary (Gass & Selinker, 2001).

Semantics. Semantics is the study of meaning. Knowledge of the semantics of a language also includes knowledge of the reference of words, word combinations, and limitation of word meanings. For example, in English the word bank has multiple meanings. When a reader encounters the word bank in text such as “The children sat very close to the river bank admiring the elegant movements of the swans,” he knows from the context that the word bank is being used to represent a margin. Knowing that words may have multiple meanings, and knowing those meanings, allows listeners and readers to interpret messages appropriately. Word combinations also affect the meaning of a sentence. For example, the meaning of the sentence: “The dog bit the man” is different from the meaning of “The man bit the dog” although both sentences include exactly the same words.

Pragmatics. Pragmatics refers to the way language is used in context. For example, when a teacher says: “Eyes on me,” a direction is being given and the expectation is that students will look at the teacher. The teacher is not suggesting she has eyes on her body somewhere. Word order has also an effect on pragmatics. For example, when a child orders a chocolate and vanilla ice cream cone, the order of the flavors may be important to understand which flavor comes first and which comes second.

The level of importance of each of these elements varies at different points in the development of language proficiency. A mature speaker of a second language uses the language differently from a novice speaker, and the differences follow predictable stages of development. For example, reading development depends on knowing the sounds in words and being able to accurately read words contained in text. Similarly, understanding the pragmatics of a language requires that second language learners understand phonology, morphology, and semantics.


Several linguistic models attempt to explain the development of second language acquisition. The three most common models are the Universal Grammar Model, the Competition Model, and the Monitor Model. The Universal Grammar Model refers to the system of principles, conditions, and rules that are properties or elements of all human languages. At the same time, each language has grammatical rules that vary from one language to another. Thus, different languages have a limited possibility of different grammatical structures (Chomsky, 1975). Therefore, second language learners base their second language acquisition on universal principles common to all languages, and on the constraints of the particular rules of each language. For example, adjectives in English usually precede nouns. By contrast, in Spanish adjectives follow nouns. Although adjectives in both languages have the same function, their position depends on the constraints of each of the languages.

The Competition Model is based in the assumption that forms of natural language are created to communicate. Thus, second language learners are faced with the conflict between native language and target language cues and cue strengths. Learners will first resort to their native language interpretation strategies, and when these do not match the target language, then they resort to a universal selection of meaning based on cues as opposed to syntax-based cues. Positive and negative evidence is necessary for learners to realize which cues are correct for the target language (Bates & MacWhinney, 1982).

The Monitor Model (Krashen, 1985) has been very influential in school settings. This model is based on five hypotheses: the Acquisition-Learning Hypothesis (acquisition occurs unconsciously, learning is conscious knowledge of the second language); the Natural Order Hypothesis (language rules are acquired in a predictable order); the Monitor Hypothesis (the learned system acts as a monitor of the acquired system), the Input Hypothesis; and the Affective Filter Hypothesis (motivation, attitude, self-confidence, and anxiety affect second language acquisition).

Krashen's 1985 Input Hypothesis, central to his theory of second language acquisition, suggests that language instruction just slightly above the student's current level of language proficiency (i.e., comprehensible input) is useful for second language acquisition. Generally, a silent period in the beginning of second language acquisition is natural and desirable until learners feel comfortable expressing themselves. Speaking cannot be taught directly; it is a result of internalizing comprehensible input.

Cummins (1979) hypothesized that second language acquisition includes the development of two proficiencies, conversational skills and academic language. Conversational skills (also called Basic Interpersonal Communication Skills, BICS) refer to the ability of children to use everyday language with adults and peers. The more formal academic language is the language of the classroom, as it is frequently characterized. Academic language enables students to understand and apply academic content in school. Conversational language is easier to learn and is learned more quickly than academic language.


Second language learners in the United States are typically referred as English language learners (ELLs). According to the National Research Council (1998), ELLs are “students who come from language backgrounds other than English and whose proficiency is not developed enough where they can profit fully from English-only instruction” (August & Hakuta, 1997, p. 15). The term Limited English Proficiency (LEP) is the formal term used by the federal government to describe and identify ELLs. The term ELLs is considered more descriptive and less pejorative than other terms (LaCelle-Peterson & Rivera, 1994; August & Shanahan, 2006). Approximately 67% of ELLs are in elementary school settings (Kindler, 2002). This statistic means that over 3 million ELLs attend elementary schools, representing more than 11.7% of the elementary school population. The vast majority of ELLs speak Spanish (79.2%) as their first language, but there are more than 460 native languages spoken by school-age students nationwide. The largest language groups after Spanish are Vietnamese (2%), Hmong (1.6%), Cantonese (1%), and Korean (1%) (Kindler, 2002).

Approximately two out of every three ELLs reside in five states: California, Texas, New York, Florida, and Illinois. Despite this concentration of ELLs in specific states, virtually all states in the United States have seen dramatic increases in their ELL populations since 1990 when the wave of immigration to the United States rose substantially. Many of these states are experiencing the emergence of ELLs in significant numbers for the first time.

For a high percentage of ELLs, schools have difficulty providing the learning environments necessary for them to succeed academically and keep pace with their native English-speaking peers. A major challenge is teaching ELLs a second language (i.e., English) and academic content simultaneously. Since 1998 the federal government has tracked the progress of ELLs as a separate group on the National Assessment of Educational Progress. In important subjects such as reading and math, ELLs lag considerably behind other students. How to close this achievement gap concerns the research community and bilingual educators (August & Shanahan, 2006).


A central question regarding ELLs acquiring English as a second language is whether it is better to teach them English language and academic content directly in English or to first make sure they have developed literacy skills in their first language. A number of research syntheses have been conducted to address this question. Francis, Lesaux, and August (2006) reviewed these syntheses and also conducted their own analysis. Although the quality of this research is not particularly strong, Francis, Lesaux, and August concluded there is a benefit to literacy development in English when ELLs are instructed in their native language (Francis et al., 2006). Overall, native language instruction resulted in a small positive impact on English reading development. They also noted the effect was strongest in those studies that paired native language instruction with English literacy instruction.

Regardless of the timing of English instruction in relation to primary language instruction, it is essential that English is taught with a strong focus placed on both learning the language and learning academic content in that language. In terms of academic content, much of the instructional approaches that are effective for native English-speaking students should also be effective for students learning English as a second language. For example, Sha-nahan and Beck (2006) concluded that in terms of English literacy development, the core instructional components that are effective with native English speakers, such as phonemic awareness, phonics, fluency, vocabulary, and comprehension, are effective with students learning English as a second language. Further, many of the same instructional approaches that are effective in delivering instruction with native English speakers, such as instruction that is systematic and explicit, will be effective with second language students.

In terms of acquiring English as a second language, approaches referred to generally as sheltered instruction, in which students learn English under conditions of high language support, are advocated. In sheltered instruction, the English demands are lower than they are for native English speakers, and the acquisition of English is promoted through instruction in the language and instruction in academic content simultaneously. Frequently, however, explicit instruction in English gets less emphasis and it is more a hope that “language develop occurs” (Gersten & Baker, 2000, p. 459) during content area lessons than a clear instructional objective. This circumstance can pose a particular problem when teachers are required to cover extensive content in science, social studies, and mathematics, and there is insufficient time for English language development, particularly formal academic English.

Although the research on specific instructional variables that affect second language learning is minimal, five variables have some empirical support as well as conceptual merit: (a) vocabulary as a major curricular objective, (b) using visuals to reinforce concepts and vocabulary, (c) implementing cooperative learning and peer-tutoring strategies, (d) using native language strategically, and (e) modulation of cognitive and language demands (Gersten & Baker, 2000). Vocabulary is a key instruction target in second language learning. Vocabulary instruction should include concentration on Tier 2 words, (i.e., words that are likely to appear in a wide variety of texts and in the written and oral language of mature users (Beck, 2002). However, second language learners in the initial stages of language acquisition also benefit from instruction in Tier 1 words (i.e., words that are common in everyday life) because they frequently are not familiar to second language learners.

Using visuals and prompts helps learners visualize the abstractions of language and provide second language learners with the opportunity to practice vocabulary in formats such as small group instruction. Instructional interactions with peers increases the likelihood that information will be retained. In modulating cognitive and language demands, skillful teachers increase second language demands when students are practicing familiar academic content and decrease language demands (e.g., the use of complete sentences) when instruction focuses on the learning of new content. Strategic use of the student's native primary language in learning new content can help second language learners attach new labels to concepts they know in their primary language. One problem in using the student's native language to explain concepts is that sometimes second language learners do not understand the concept in their primary language. As of the early 2000s, research in all of these areas is badly needed.


School-based assessments of students learning a second language are done for two broad purposes: to assess their English language proficiency and to assess their academic content knowledge. A number of problems are associated with both types of assessments, although they can provide information that is useful in school decision-making, such as identifying students for academic programs. For example, measures of English language proficiency do not predict very accurately performance on academic measures. Assessments of language proficiency also may underestimate how well students are prepared academically because performance of second language learners on academic assessments may be influenced by their knowledge of English.

Thus, low language proficiency may obscure what the learner really knows about the academic content being assessed. For example, in the early elementary grades, measures of language proficiency in English are sometimes used to delay literacy instruction until students have acquired the oral language skills considered necessary to learn academic content. A common assumption has been that teaching reading in English should occur after oral language proficiency is developed. Empirical evidence contradicts this position. Measures of oral English proficiency do not predict how well second language learners will learn English literacy skills. Even students whose oral English is very low can make significant progress learning foundations of reading in a second language such as phonemic awareness and understanding of the alphabetic principle (Chiappe, Siegel, & Wade-Woolley, 2002; Geva & Yaghoub Zadeh, 2006; Lesaux & Siegel, 2003).

In the United States, second language instruction has been heavily influenced by Krashen's 1985 input hypothesis. However, this hypothesis has been criticized for being vague in terms of instructional specificity and lacking empirical support. Many studies have shown that speaking helps comprehension and acquisition of a second language (Pica et al., 1987; Ellis et al., 1994; Gas & Varonis, 1994; Klingner & Vaughn, 1996; Mackey, 1999). Further, in school contexts, Klingner and Vaughn (1996) suggest that providing students plenty of opportunities to practice newly learned vocabulary words in complete sentences in different contexts throughout the school day, providing immediate feedback and frequent monitoring, helps children increase English language acquisition. In fact, several researchers have found that a major issue in instructional contexts is the lack of opportunities second language students have to use English in the classroom (Arreaga-Mayer & Perdomo-Rivera, 1996; Gersten & Baker, 2000; Ramírez, 1992). In other words, the lack of opportunities for students to engage in meaningful language use that is cognitively challenging may hinder second language acquisition.

Another issue extensively discussed has been whether there is a critical period in second language learning, generally considered to be around puberty, beyond which it is difficult or impossible to learn a second language to the same degree as a native speaker. This hypothesis suggests that young children are more likely to attain nativelike proficiency in a second language than are adolescents or adults. Children appear to master the phonology of a language faster than adults, but adults appear to learn morphology and syntax faster.

However, the advantage children appear to have in attaining mastery of a second language (particularly phonology) is not uniformly apparent in all languages. Learning a second language is influenced by the alignment between the native language and the second language, and mastery of skills in the native language influences second language acquisition.


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