Evidence primarily exists in adults that engaging in task‐related mental activity after new learning results in increased forgetting of learned information, compared with quietly resting in the minutes that follow learning, where less forgetting is observed. The current study investigated whether the beneficial effect of post‐encoding rest can be observed in children aged 13–14 years. Each child ( N = 102) encoded two word lists. After the presentation and immediate recall of one word list, children wakefully rested for 10 min (resting condition), after presentation and immediate recall of the other word list, they solved visuo‐spatial problems for 10 min (problem‐solving condition). Seven days later, a surprise free recall test for the two word lists took place. Our results showed that children retained more words over 7 days in the resting condition than with the problem‐solving condition. Post‐hoc analyses revealed that the resting effect was a function of the number of words recollected during the immediate recall. Specifically, those children who recalled fewest words (≤ 13/30 words) in the immediate recall showed a significant resting effect. There was no resting effect in those who recalled a mid‐range (14–16/30 words) or a high number (>16/30 words) of words. These results provide new insights into the factors that influence memory in children, and suggest that a few minutes of wakeful rest benefits memory, relative to engaging in an ongoing task. Statement of contribution What is already known on this subject? Task‐related mental activity after encoding weakens memory retention more than wakeful resting. Beneficial effect of resting after encoding was found primarily in younger and older adults. What does this study add? We investigated children at the age of 13–14 years. 8‐min post‐encoding wakeful resting supports memory retention over 7 days. Individuals differ in the impact of a brief period of wakeful resting after learning. Only children with lower immediate memory performances profited from wakeful resting.