We investigated the role of rehearsal in verbal working memory (WM) and whether WM capacity can be improved by a rehearsal instruction in very old age. In two experiments, we tested a total of 78 old–old adults (75 years and above) in one experimental session consisting of three assessment phases. First, participants worked on three different WM span tasks to assess their baseline performance. In the next phase, half of the participants received a rehearsal instruction to practice on two of the WM tasks, whereas the other half received no strategy instruction (Experiment 1) or worked on a filler task (Experiment 2). In the final phase, participants again worked on the three WM tasks. In Experiment 1, we found significant improvements for the WM tasks over time in both groups. However, we could not find a specific improvement for the rehearsal instruction due to a high spontaneous strategy use in the control group. When minimizing spontaneous strategy use in Experiment 2 by changing the task material, we found larger improvements in the instruction compared to the control group. However, we still found substantial spontaneous strategy use in the control group. The results indicate that rehearsal, as an essential component of verbal WM, is still intact and efficient in old–old adults. Furthermore, the spontaneous strategy use indicates that old–olds use their existing skills to cope with increasing WM demands. Finally, old–old adults benefited from an explicit rehearsal instruction showing potentials to boost WM capacity in this age group.