The present study investigated the effects of processing instruction (PI) on the acquisition of accusative case markers in German, focusing on whether PI influences learners’ online processing behaviors. Third and fourth semester L1 English-L2 German learners were divided into two groups: a traditional instruction (TI) group and a PI group. Participants completed offline sentence interpretation and production tasks, as well as a self-paced reading (SPR) task, which provides a detailed investigation of how PI alters processing strategies. Results showed that the PI group outperformed the TI group on the sentence interpretation task and matched their performance on the production task. The SPR task revealed that, in some conditions, the PI group showed increased attention to and processing of accusative case markers after training, while the TI group did not. The results provide some support for the claim that PI is effective because it alters learners’ processing strategies.