We conducted a modified cluster randomized controlled trial examining Story Detective, a multicomponent listening comprehension intervention, with 351 students (47% girls; pretest Mage = 5.55; 39% Hispanic, 32% White, 16.5% Asian-American, 6.8% multiracial, 2.6% African-American) in the U.S. Classes were randomly assigned to Story Detective or business-as-usual conditions. Results showed significant effects for Story Detective on proximal vocabulary (g = 1.28), comprehension monitoring (g = 0.27), and distal grammatical knowledge (g = 0.26), but not on distal listening comprehension. Students with stronger initial vocabulary benefited more. Classroom observations revealed business-as-usual instruction included vocabulary and inferential questioning but lacked comprehension monitoring and grammatical instruction-precisely where significant effects occurred. Findings suggest multicomponent interventions improve specific skills, but transfer to comprehension may require extended implementation.