Simultaneous interpreting (SI) is an intensive multitasking activity that requires coordination of a variety of linguistic and cognitive control mechanisms. Research has shown that interpreters perform better in tasks that require domain-general executive functions (EF), but the question remains whether such cognitive alternation is a result of interpreting experience or it reflects a selection bias that only cognitively capable people are recruited and trained to be interpreters. We examined the cognitive changes experienced by beginner-level students engaged in an intensive, two-week interpreting training programme. Our findings show that: (a) only cognitive flexibility was enhanced by training, together with improvement in SI performance; (b) the three EF subcomponents in their pre-existing forms negatively correlated with training gains; and (c) only pre-existing cognitive flexibility was positively associated with improvement in SI performance. Findings were discussed regarding the relationship between cognitive abilities and the early-stage acquisition of interpreting.