Considering, that most psychological research tests hypotheses by comparing average effects across the sample, it is often overlooked that effects may vary between individuals. Combined experimental and correlational approaches are needed to better test and revise theories of long-term memory, but also to better understand the needs of the individual to support successful learning. Here, we use the example of sensory processing sensitivity (SPS) to demonstrate how individual differences can contribute to a learning-experiment and shed new light on inconsistent findings regarding beneficial effects of post-learning wakeful rest. SPS describes a temperament trait associated with greater reactivity to and deeper processing of environmental stimuli. In this experiment, we tested whether and how individual differences in SPS contribute to differences in long-term memory consolidation depending on the activity following learning. Sixty-four participants encoded and immediately recalled two word lists followed by two conditions: Either an 8-minute delay of wakeful resting or by performing an attention task. In a second experimental session after 7 days, participants completed a surprise free recall test for both word lists and a SPS-questionnaire. Similar to some recent studies, we did not replicate an overall beneficial effect of wakeful rest on memory retention. However, higher (vs. lower) SPS participants benefited more from the wakeful resting delay, while their memory retention was also more hindered by the attention task. Thus, post-learning activity affects individuals’ memory retention to varying degrees. While it had only minor effects on lower SPS individuals’ memory retention, it affected high SPS individuals much more.