Brown prof's AI cheating test: grades crash from 96% to 48%

When Roberto Serrano’s take-home midterm averaged 96 percent, he knew something was off. The Brown University economics professor had been teaching the course for years, and scores typically hover between 65 and 80 percent. So he did what any suspicious instructor would do: he fed the questions into ChatGPT. The AI’s answers matched his students’ work almost exactly, right down to a strangely convoluted mathematical proof that most humans wouldn’t choose.

The real reckoning came with the final. Serrano made it a proctored, in-person exam. Eighteen of his 86 students dropped the course before test day, and nine others simply didn’t show up. The class average crashed to 48.6 percent — the lowest score he’s ever recorded. Nineteen students failed outright. Serrano voided the midterm entirely and made the final worth 80 percent of the grade. Brown’s administration told him to report each cheating case individually, a response he called “meek” and “ridiculous.”

This isn’t one professor’s anecdote. Two large-scale studies back up the pattern with hard numbers. A Chinese study tracking over 26,000 students in grades 7 through 12 found that six months after students gained access to AI tools, homework scores shot up 18 percent while completion time dropped from 64 to 45 minutes. Exam scores, meanwhile, fell by 20 percent. On high-stakes entrance exams, the hit was even worse — an 18 to 24 percent decline that took about two years to fully materialize. Top students suffered most, losing nearly a quarter of their performance.

A UC Berkeley study examining more than 500,000 grades at a Texas research university tells a similar story. After ChatGPT launched, courses heavy on writing and programming assignments saw a 13 percentage-point jump in A grades. When researchers compared homework-heavy courses to exam-heavy ones, the gap hit 16 percentage points. The message is unambiguous: unsupervised assignments are now an AI free-for-all. Serrano put it bluntly to Inside Higher Ed: “We cannot afford to have a society in which a significant fraction of our best young minds think that cheating is OK. That leads to a declining society, to a failed society.”