Self-reported AI usage rose from near zero to about 80 percent over the study period, with a big jump coinciding with the releases of DeepSeek V2.5 in September 2024 and DeepSeek R1 in January 2025. The most popular tools were Doubao, DeepSeek, ChatGLM, Ernie Bot, and Qwen.
Homework scores climb 18 percent and completion time drops from 64 to 45 minutes, while closed-book exam scores plunge by 20 percent. | Image: Strömberg et al.
The study takes advantage of the fact that students discovered AI on their own at different times. The authors use a difference-in-differences design, a method that measures the change in outcomes for a treated group before and after an intervention and subtracts the change over the same period for an untreated comparison group.
Here, they track how each student's performance shifted before and after they started using AI, then contrast that trend with students who weren't using AI yet. The timing of first use comes from self-reported data, and the causal claim assumes both groups would have developed similarly without AI.
Better homework, worse test scores
