Definition:
Individual differences (IDs) in second language acquisition refer to the set of learner-internal variables that explain variation in learning outcomes among individuals exposed to similar input and instruction. The major individual difference variables are language aptitude, motivation, language anxiety, age (age effects in SLA), cognitive style, personality traits, and learning strategies. Individual differences research addresses the fundamental question: Why do some learners succeed while others, in apparently the same conditions, do not?
In-Depth Explanation
The Major Variables
Language Aptitude
Language aptitude is the set of cognitive abilities that predict rate and ultimate success in language learning — phonemic coding ability, grammatical sensitivity, inductive language learning ability, and working memory capacity. Aptitude is the single strongest predictor of L2 achievement in instructed settings.
Motivation
Motivation encompasses the reasons for learning, the intensity of effort, and persistence over time. Key frameworks include Gardner’s integrative/instrumental distinction, Dörnyei’s L2 Motivational Self System, and self-determination theory. Motivation is the strongest predictor in naturalistic/self-directed settings.
Anxiety
Foreign language anxiety — fear of negative evaluation, communication apprehension, and test anxiety — consistently correlates negatively with achievement. Even skilled learners with high aptitude underperform when anxiety is high.
Age
The Critical Period Hypothesis and age effects in SLA address whether age constrains ultimate attainment. Earlier exposure generally advantages pronunciation; the relationship to grammar and vocabulary is more complex. See also sensitive period.
Cognitive Style and Personality
Cognitive style (field-dependent vs. field-independent), tolerance of ambiguity, extroversion/introversion, and willingness to communicate all influence learner behavior and, indirectly, outcomes.
Learning Strategies
Learning strategies — metacognitive, cognitive, social, and affective strategies — are partially trainable behaviors that mediate how learners process input and practice output.
Interactions, Not Isolation
Individual differences do not operate independently. A learner with high aptitude but low motivation may underperform one with moderate aptitude but fierce motivation. Anxiety interacts with aptitude — anxious learners cannot deploy their aptitude effectively. This interaction complexity is why single-variable studies often explain limited variance.
Aptitude-Treatment Interaction
Peter Skehan and others have explored aptitude-treatment interaction — the idea that different instructional methods work better for learners with different aptitude profiles. High-aptitude learners may benefit more from explicit instruction; lower-aptitude learners may need more implicit, input-rich approaches.
Key Researchers
- Zoltán Dörnyei — Comprehensive framework for IDs in SLA; motivation research
- Peter Skehan — Language aptitude and task-based research
- Robert Gardner — Motivation and attitude in SLA
- Rebecca Oxford — Learning strategies classification