Learnability

how easy or difficult it is for learners to acquire a particular feature of language

Factors influencing learnability

 * How similar or different a feature is from the learner's first language
 * Whether a structure is text-external or text-internal
 * The salience of the feature
 * How noticeable the feature is in a text or an utterance
 * Whether the feature is frequent or infrequent in the target language
 * The relative importance of the feature to understanding input
 * How well the meaning is supported by context

Bruntt, Karen and Bryanne, Ulla. Handbook for Grammar Detectives, page 28-30