Incidental word learning while reading: a meta-analysis

A meta-analysis of 20 experiments examining incidental word learning during normal reading shows that students learn around 15% of the unknown words they encounter A test of homogeneity indicates that study outcomes diverge, although their heterogeneity is relatively small (19%). An exploratory multi-level analysis of the variability in the results suggests that several factors affect the probability of learning an unknown word while reading: pretest sensitization, students' grade level, students' level of reading ability, the sensitivity of assessment methods to partial word knowledge, and the amount of text surrounding the target words. A model that contains students' grade level and assessment methods' sensitivity to partial word knowledge predicts 66% of the systematic variance in the effect sizes. Implications for research and instruction are discussed.