The roles of phonological short-term memory (pSTM) and speech perception in spoken sentence comprehension were examined in an experimental design. Deficits in pSTM and speech perception were simulated through task demands while typically-developing children (N = 71) completed a sentence-picture matching task. Children performed the control, simulated pSTM deficit, simulated speech perception deficit, or simulated double deficit condition. On long sentences, the double deficit group had lower scores than the control and speech perception deficit groups, and the pSTM deficit group had lower scores than the control group and marginally lower scores than the speech perception deficit group. The pSTM and speech perception groups performed similarly to groups with real deficits in these areas, who completed the control condition. Overall, scores were lowest on noncanonical long sentences. Results show pSTM has a greater effect than speech perception on sentence comprehension, at least in the tasks employed here.