This study investigates relations between second language (L2) lexical input and output in terms of word information properties (i.e., lexical salience; Ellis, 2006a). The data for this study come from a longitudinal corpus of naturalistic spoken data between L2 learners and first language (L1) interlocutors collected over a year's time. The corpus was analyzed using word information properties related to concreteness, familiarity, and meaningfulness to examine word repetitions between input and output, correlations between the input and the output, linear trends over time, and whether lexical properties in the output were predictive of growth in TOEFL scores. The results indicate that L2 learners are more likely to repeat word types found in L1 input and that L1 interlocutors and L2 learners follow similar linear trends over time such that words with lower concreteness, lower familiarity, and lower meaningfulness were produced over the course of the study in both the input and output. A linear mixed model analysis showed that decreases in concreteness scores explained significant gains in TOEFL scores over time. The findings from the study indicate strong associations between L2 input and output and provide evidence linking development in word information properties to development in academic English proficiency.