ABSTRACT: Word learning can build the high-quality word representations that support skilled reading and language comprehension. According to the partial knowledge hypothesis, words that are partially known, also known as "frontier words" (Durso & Shore, 1991), may be good targets for instruction precisely because they are already familiar. However, studies investigating this question have produced mixed findings, and individual differences in baseline knowledge have complicated results both within and across studies. We present two studies that took a different approach, controlling both familiarity and the nature of the familiarizing episode. We controlled familiarity with novel words through pre-exposure ("pre-familiarization") in isolation, to induce form-based familiarity, or in sentences that provided few clues to meaning, to induce partial semantic knowledge. The number of pre-exposures varied (0, 1, or 4). After the pre-familiarization phase, we presented the words in several highly informative sentences to support meaning acquisition. Participants included both adults and typically developing children, ages 9-12. Participants' self-rated familiarity with target words, and their knowledge of the words' meanings and orthography were each measured at baseline, immediately after learning, and one week later. Orthographic and semantic word learning showed contrasting effects of pre-familiarization. For orthographic learning, it was the number, rather than the type, of pre-familiarizations that mattered most. By contrast, the number of pre-familiarizations had little impact on word semantic learning; further, pre-familiarization in low-constraint sentences did not consistently boost subsequent learning. These findings suggest that familiarity with a word prior to instruction does not necessarily improve word-learning outcomes, and they highlight the importance of repeated exposures to high quality contexts for robust word learning.
