The most relevant theory that ESL teachers need to know is called the Developmental Interdependence theory. This theory suggests that a child’s second language acquisition and competence partly depends on the level of competence the child has in their first language. In other words, the more the child knows in their first language, the easier and quicker it will be for the child to develop their second language. The reason for this is that the ESL student transfers their knowledge from the first to the second language. An example of this is vocabulary knowledge. When learning a second language, the ESL student transfers vocabulary knowledge from their first language to their second. Therefore, the more vocabulary words a student knows in their first language, the easier and faster it will be for the student to acquire proficiency in their second language (and the easier it will be for ESL teachers to teach these students!) When a student’s vocabulary knowledge is weak in their first language, then the student must be explicitly taught the meaning of the vocabulary word and the language for that word.This makes learning a second language more difficult and more time consuming.
The Developmental Interdependence theory stresses language in general for the success of learning a second language. As a parent or an ESL teacher, the emphasis on your child's/student’s native language is key. Therefore, as an ESL teacher, it is important to inform parents to teach their children as much of their first language as possible. This will make their first language strong and will therefore result in a strong second language. If parents are able, giving lists of academic vocabulary words for parents to pre-teach to their children may be helpful. Encouraging parents to read with their child can also help develop their child's vocabulary. Stressing the importance of your students’ first language could be a topic to discuss during Open House and parent/teacher conferences. The Developmental Interdependence theory challenges the English only policy that is sometimes supported in monolingual schools where the majority language is English. The Developmental Interdependence theory suggests that English is not the key, but a strong first language is.
Supporting the Developmental Interdependence theory is the current theory about bilingualism and the thought system behind learning languages. This theory is called the Common Underlying Proficiency Model (CUP). The CUP suggests that both languages function within the same system. This model also states that humans are able to store two or more languages and there is no limit for learning another language or multiple languages in the brain. The CUP supports the evidence that bilinguals are able to use both languages with ease and can transfer knowledge from one language to their other language. The CUP also supports the Developmental Interdependence theory in that the student is able to transfer their knowledge from their first language to their second. An example of transferring between languages is codeswitching.
An outdated theory about bilingualism states that there is limited room in the brain for learning two or more languages.This false theory is called the Separate Underlying Proficiency (SUP). This theory states that each language acts separately from one another. For example, for a bilingual child learning English and Spanish, one operating system stores and uses English and the other operating system stores and uses Spanish. Each language area is separate from one another and do not interact or work together.
Bilingual Education:
The Thresholds Theory states that cognitive advantages of bilinguals depend on the level of competence in each language. A child must reach a certain level of proficiency to avoid negative consequences of bilingualism. The child must then reach a second threshold, or level of competence, to experience the positive benefits of bilingualism. It is believed that the Thresholds Theory helps to explain why bilingual children in bilingual immersion classes experience a delay at first when learning their second language. The bilingual students’ proficiency in their second language catches up to the proficiency in their first language. As a result, the students become balanced bilinguals. Once these students’ second language develops to a certain level of proficiency where students are able to comprehend academic language in the classroom, these students begin to benefit from being bilingual. Research suggests that balanced bilinguals surpass their monolingual peers.