Prospective memory (PM) refers to the cognitive processes associated with remembering to perform an intended action after a delay. Varying the salience of PM cues while keeping the intended response constant, we investigated the extent to which participants relied on strategic monitoring, through sustained, top–down control, or on spontaneous retrieval via transient bottom–up processes. There is mixed evidence regarding developmental improvements in event-based PM performance after the age of 13 years. We compared PM performance and associated sustained and transient neural correlates in 28 typically developing adolescents (12–17 years old) and 19 adults (23–30 years old). Lower PM cue salience associated with slower ongoing task (OT) RTs, reflected by increased μ ex-Gaussian parameter, and sustained increases in frontoparietal activation during OT blocks, both thought to reflect greater proactive control supporting cue monitoring. Behavioral and neural correlates of PM trials were not specifically modulated by cue salience, revealing little difference in reactive control between conditions. The effect of cue salience was similar across age groups, suggesting that adolescents are able to adapt proactive control engagement to PM task demands. Exploratory analyses showed that younger, but not older, adolescents were less accurate and slower in PM trials relative to OT trials than adults and showed greater transient activation in PM trials in an occipito-temporal cluster. These results provide evidence of both mature and still maturing aspects of cognitive processes associated with implementation of an intention after a delay during early adolescence.