This study examines the effects of low- and high- cognitive demand discussion on children's story comprehension and identifies contributions of discussion, initial vocabularies, and parent reading involvement. A total of 70 English learner preschoolers took baseline vocabulary tests in Portuguese and English, were randomly assigned to experimental or control conditions, and were read pairs of books in small groups. In the experimental condition, 1 book per pair was discussed using low- cognitive demand (literal) talk. The other was discussed using high-cognitive demand (inferential) talk. In the control condition, books were read aloud without discussion. All children took story comprehension tests (new literal and inferential questions) following books' third readings. Findings showed significant effects of discussion on comprehension. Repeated measures analyses indicated significant effects of high-demand discussion on both question types, particularly inferential questions. Regression indicated significant contributions of high-demand discussion beyond English vocabulary and home reading. Practice or Policy: High-demand discussion significantly influences chigldren's inferential thinking skill, contributes benefits over and above expected impacts of initial vocabulary, and may offer benefits over low-demand talk for literal details. Teachers need not wait to engage young language learners in cognitively challenging discussion. (author abstract)