Second language acquisition (SLA) and second language testing (LT) both focus on “what” and “how” issues of language: SLA is concerned with what the learner's language is at a given point and how further language can best be acquired, and LT is concerned with what language ability (knowledge) is and how it can best be measured. This chapter examines the extent to which each discipline can benefit from advances made in the other, using the example of discourse. It begins by focusing on the contribution of LT to SLA, with emphasis on the following areas: (a) defining the construct of language ability, (b) applying findings from LT to confirm and/or test SLA hypotheses, and (c) providing SLA researchers with quality criteria for tests and tasks. We then turn to the contribution of SLA to LT, focusing on: (a) identifying the language components that need to be elicited, (b) proposing innovative tasks that can be used for language assessment, and (c) informing language testers about language variations so tests can be constructed accordingly. Each of these contributions is discussed using the case of discourse.

Contributions of LT to SLA

Defining the construct of language ability

While SLA researchers have focused on the description of the learner's language, language testers have concentrated on the definitions and theory of language ability. Valid theories of language ability can be useful for SLA researchers in examining the validity of the findings about second language acquisition, that is, the extent to which the second language has actually been acquired.