The first, second, and the third chapters of the book focus on the question of whether word learning can function as a predictor of language proficiency achievement. The purpose of the studies was to formulate mathematical models to prognosticate the performance of high school learners on the End of the Course Achievement (ECA) tests. The last chapter deals with vocabulary learning mainly gained through L1 equivalent rote memorization, i.e., paired associate learning, and the learners' ability to transfer the lexical knowledge acquired as such into L2 reading comprehension context of use.