Recalling previously learned information enhances subsequent learning of new information. This forward testing effect (FTE) has been scarcely examined with complex text materials. The underlying mechanisms of the FTE are still unclear, especially regarding the potential role of extrinsic motivation. We tested the hypothesis that the FTE is partially related to enhance participants’ motivation to retrieve all previously learned information, and that this achievement motivation can be manipulated by providing an external reward. The present study investigated the moderating effect of extrinsic motivation on the FTE, using a 2 (interim learning task: retrieval vs. restudy) × 2 (external motivation: high vs. low) between-subjects design in a digital learning setting. More specifically, participants studied three text sections; after Texts 1 and 2, they restudied or recalled the previously learned text information. All participants took a final free-recall test after Text 3. Briefly before the final test, participants were instructed that the best-performing 10% of the students (high motivation group) versus a random selection of 10% (low motivation group) would receive 10 Euros. Consistent with the hypothesis, we observed that retrieval practice enhanced recall of Text 3, replicating the FTE for complex materials in a digital learning setting. Critically, the size of this FTE was moderated by the level of extrinsic motivation: The FTE was reliable for the low motivation group but vanished for the high motivation group. This finding supports motivational theories of the FTE by demonstrating that participants’ motivational level is critical in a digital learning setting.