Intellectual (cognitive) development, the emergence of increasingly sophisticated forms or levels of understanding, reasoning, and rationality is an ongoing process of reflection, coordination, and social interaction that begins in early childhood and continues, at least in some cases, long into adulthood (Moshman, 2003). In this process, language is a primary tool in the entire life. However, it is not to say that thinking (as an intellectual ability) cannot take place without language (Munn, 1951), but rather mostly, thinking is mediated by language and thus develops to a much higher level of sophistication. The intimate link between language and cognitive development forms the core of the present article. It focuses on the important contribution of mother tongue in the process of cognitive development. Two major theories of development: Piaget and Vygotskys' views are investigated in relation to language. It is concluded that, although thought is the base, language intellectualizes it to a great deal.