The sheer quantity of words known (breadth) is strongly predictive of reading comprehension, yet little is understood about how quality of word knowledge (depth) affects comprehension. A group of 35 bilingual and monolingual 5th-grade students worked on developing depth of knowledge of 8 words, culminating in an activity in which the students produced captions for images related to each word. The captions were scored using a 4-point depth scale, and similarities and differences between bilingual and monolingual students were assessed. Results indicated a significant effect of depth of word knowledge in predicting reading comprehension, particularly for students with average to strong oral language skills. (Contains 1 footnote, 6 tables, and 1 figure.)