This paper discusses the pedagogical implications of Dynamic Systems Theory approaches to second language development. The main question addressed is whether it is possible to describe a learner's level of proficiency with a simple and unambiguous label, and if so, whether the CEFR can provide such a label. It is argued that considering the dynamic and multidimensional nature of second language development, only an approach that values the relevance of variability will be able to capture the crucial time dimension of development. When learning is defined as self-organization that follows the perturbation of a system, language learning cannot be seen as development that follows a predetermined sequence, but must ultimately be regarded as a contextualized individual trajectory. When this observation is applied to language teaching and language testing, it must be concluded that a longitudinal approach using a language portfolio that captures a range of language skills as proposed by the CEFR is of considerably greater value for the learner than a rigid assessment of some aspects of language proficiency at one moment in time.
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