Researchers investigated whether sleep-dependent memory consolidation could help to save practice time during relearning.
During two sessions occurring 12 hr apart, 40 participants practiced foreign vocabulary until they reached a perfect level of performance.
Half of them learned in the morning and relearned in the evening of a single day.
The other half learned in the evening of one day, slept, and then relearned in the morning of the next day.
Their retention was assessed 1 week later and 6 months later.
The researchers found that interleaving sleep between learning sessions not only reduced the amount of practice needed by half but also ensured much better long-term retention.
Sleeping after learning is definitely a good strategy, but sleeping between two learning sessions is a better strategy.