In SLA, L2 learning is typically broken down into six skills--speaking, listening, reading, writing, grammar and vocabulary. In my context (EFL), some would like to define success with instruments such as the paper-based TOEFL test, a norm-referenced test of receptive skills--grammar, listening and reading.
Can one become highly proficient in receptive skills without building productive skills of speaking and writing, or is there a threshold that cannot be moved beyond if there are deep weaknesses in some of these six main skills?
Does a weakness in one of these skills necessarily hinder the other skills from developing?
Is the idea that all skills must be brought up together controversial, or is this a basic principle that language teachers and learners must come to grips with?