Pica, T.  (1994).  Questions from the language classroom:  Research perspectives.  TESOL Quarterly, 28.  pp.49-79.

10. What can be done for L2 learners who seem to have reached a plateau in their learning?
 

• While some researchers attribute "fossilization" to a lack of opportunities for integration, others argue that an overemphasis on communicative activities results in learners who are functional but grammatically inaccurate.

 
• Schmidt and Frota (1986) found that often learners who are functional do not notice the differences between their utterances and those of more accurate speakers.

 
• Areas that seem to be particular sources of inaccuracy is grammatical morphology (Bardovi-Harlig & Bofman, 1989) and sociolinguistic appropriateness (Swain & Lapkin, 1989).

 
• The above mentioned research indicates that more grammar-based materials might be a very useful part of the language classroom

 

References
Bardovi-Harlig, K., & Bofman, T.  (1989).  Attainment of syntactic and morphological accuracy by advanced second language learners.  Studies in Second Language Acquisition, 11(1), 17-34.

Schmidt, R.W., & Frota, S.N.  (1986).  Interaction, acculturation, and the acquisition of communicative competence:  A case study of an adult.  In N. Wolfson & E. Judd (Eds.), Sociolinguistics and language acquisition (pp. 137-174).  Rowley, MA:  Newbury House.

Swain, M., & Lapkin, S. (1989).  Aspects of the sociolinguistic performance of early and late French immersion students.  In R. Scarcella, E. Anderson, & S. Krashen (Eds.), On the development of communicative competence in a second language (pp. 41-54).  Cambridge, MA: Newbury House.