SLA research has revealed that
L2 learners, like L1 learners, pass through sequences of development.
In a given language, many of these developmental sequences are similar for L1 and L2 learners.
It is not always the case that L2 features which are heard or read most frequently are easier to learn (e.g., articles - ‘a’ & ‘the’).
Even among L2 learners from different L1 backgrounds and different learning environments, many of these developmental sequences are similar