es as an analytical aid in the context of education and that an investigation of identity construction of the students can help in understanding their educational experiences as well as academic results (Gee 2000; Sfard & Prusark 2005).
5- Bilingualism and Bilingual Education: Definition, Theory and Ideology
This section will define the concept of Bilingualism and discuss some of the theories that is related to the concept, by viewing two of the most important models of bilingualism ,which they are 'The Separate Underlying Proficiency 'and 'The Common Underlying Proficiency' , it is important to discuss the different theories about Bilingualism to have a close approach to understand how the human brain operates with two languages . Also the next part will view an example of a common challenge that faces bilingual students , and it will present a research that was made to measure the Bilingual literacy development for 3 students .
Bilingualism is the ability for a person to speak two languages, and the ability to speak more than two languages is identified as ' Multilingualism'. Grosjean (2010) defined bilingualism by emphasis on the Regular use of languages rather than fluency in every day '' Bilinguals are those who use two or more languages (or dialects) in their every day lives'' (Baker,2011).While there has been many arguments that a bilingual person should speak the two languages in the same fluency or in a balanced level , and this can be explained in the 'Balance Theory' this theory argue that in the brain there are rooms for language in the brain and the 'Monolanguage' (The first language) is bigger than the second language , so when a person receive data in the Monolanguage it won't be transferred to the second language according to Cummins (1980), who defined this idea as the 'Separate Underlying Proficiency Model of bilingualism' , he explained this term by picturing two'' languages operating separately without transfer to one another and with restricted amount of room for languages '' (Baker,2011). This theory assumes that the two languages are separated in the human brain without any interaction which proved to be untrue.
According to Baker (2011)'' the evidence suggested the opposite'', the languages are not separated in the human brain and the languages interacts and there is a transferring from a language to another. The example he gave for his argument is in the school lessons where the lessons in English they do not feed the English part of the brain only, or if the lessons are in other languages, for example, Spanish the data won't be transferred to the Spanish part only . The data learned in one of the languages can be simply transferred in the brain to the other part, so in this case a concept learned in English can be used immediately in Spanish. This idea of the of bilingualism is called Common Underlying Proficiency (Cummins, 1980, 1981) It is explained as the Iceberg Theory, where the two languages takes a part in the brain seeming to operate separately like two icebergs on a surface, but underneath the surface the icebergs melts into one direction which is the central operating system where both languages interacts an function through the same central operating system (Ibid). The main point in the Iceberg theory is the shared function of the two languages depending on one main source, which puts the two languages on the same level of sufficiency. But this is not a general bilingual law, there are many bilingual people who tend to use one of the two languages more often because they are more capable of expressing their thoughts or feelings in one of the two languages more than the other language , despite they master both languages.
The Separate Underlying Proficiency model and the Common Underlying Proficiency model of bilingualism do not give a definite idea about the function of the brain and bilingualism, and each person's brain analyze the income information and translate it to language in a different way, and most of the researches in the field of bilingualism tried to figure how does the h