There is a huge amount of academic literature talking about the relationship between language learning and content learning... CLIL scaffolding is very useful to do it simultaneously:
Wells, Gordon. The meaning makers: Children learning language and using language to learn. Heinemann Educational Books Inc., 70 Court St., Portsmouth, NH 03801, 1986.
Gibbons, Pauline. Scaffolding language, scaffolding learning: Teaching second language learners in the mainstream classroom. Portsmouth, NH: Heinemann, 2002.
Mehisto, Peeter, David Marsh, and Maria Jesus Frigols. "Uncovering Clil." China: Macmillan Publishers Limited (2008).
On the other hand, the common idea is that language is needed to knowledge building (concepts, cognitive development), but what's useful for learning language is communication and interaction.
Griffiths, Carol. Language learning strategies: Theory and research. AIS St Helens, Centre for Research in International Education, 2004. http://www.crie.org.nz/research-papers/c_griffiths_op1.pdf
Hein, George. "Constructivist learning theory." Institute for Inquiry. Available at: http://www.exploratorium.edu/ifi/resources/constructivistlearning.html (1991). http://beta.edtechpolicy.org/AAASGW/Session2/const_inquiry_paper.pdf
Language competence has sometimes been used as an idealized notion which somehow embodies the collective knowledge of a speech community in the person of an ideal speaker-hearer. Linguistic competence is an important notion of any theory of language, but one with an empirical basis. The notion of linguistic competence has to be articulated in terms of levels, domains, components, dimensions, modes etc. The core components of the grammar are included in the speaker's linguistic competence and these components corresponds to five of the major sub fields of linguistics:-
Thanks, Kiran! Do you have or know any articles which affirm that linguistic competence is an important notion of any theory of language, but one with an empirical basis?