We know that children's differences in language ability, more than any other observable factor, affect their potential for success in schooling. It is only in the last two or three decades that educationists in general have felt it necessary to state a fact that earlier educationists regarded as too commonplace to warrant stating: that language is the central achievement necessary for success in schooling. It is clear that achievement in schools is highly dependent on the child's ability to 'display' knowledge. This display almost always takes the form of spoken or written language. Child language will often be the first contact teachers have on which opinions of student potential can be based, while in the closing stages of schooling language contact through formal or informal assessments is often the only link between students and those assessors who finally declare a child's educational fate. Nor is it an artificial or improper matter that language on display is the central achievement for school success. A school curriculum is a selection of knowledge from the culture: all those things in the culture (or from other cultures) considered worth passing on through schooling. Since all forms of knowledge are 'filtered' through language, the chief item of knowledge in any culture is its language. The chief object of the school is to encourage the complete mastery of the language of the culture, since without this mastery children are denied power and influence over their own affairs and an opportunity for success in education.
Knowledge, Thought and Language Across the Curriculum.
Australian Journal of Teacher Education, 12(2).