Hypothesis
Replaying newly learned foreign words during sleep would boost recall in 11–13-year-olds even more than in adults, because slow-oscillation activity peaks in adolescence.
What failed
Words cued by loudspeaker during post-learning NREM sleep were not recalled better the next morning than uncued words. Frontal theta power rose with successful cueing as in adults, but the expected spindle-power increase did not appear.
Broken assumption
More slow-oscillation activity during sleep means cued memory reactivation works better.
Why
The paper does not settle the cause; it discusses adolescents' learning abilities and pre-sleep performance levels as possible reasons for the missing effect.
From the published paper: Wilhelm et al. Scientific Reports, 2020. ↗CC BY