Grades dropped from 96 to 48 percent when a Brown professor made students take the exam without AI

A Brown University professor suspects most of his class used AI to cheat after a take-home exam averaged 96 percent, while an in-person test produced the lowest scores ever. Two large studies confirm this pattern: where students rely on AI for homework, proctored exam scores collapse.

Roberto Serrano, an economics professor at Brown University, believes the majority of his 86 students used AI to cheat on an exam. The test was a take-home exam, and the class average came in at 96 percent. Historically, that number runs between 65 and 80 percent.

Serrano ran the questions through ChatGPT and got nearly identical answers. Many students used a convoluted mathematical proof that ChatGPT also chose, rather than the more obvious direct approach.

Serrano warned his students and made the final a proctored, in-person exam. The results proved his point. Eighteen students dropped the course, and nine didn't even show up for the test. The average fell to 48.6 percent, the worst result the course has ever seen, Inside Higher Ed reports.

Only a handful of students scored anywhere close to their take-home results. Nineteen students failed outright. Serrano voided the midterm and weighted the final at 80 percent of the course grade.

The university's response was "meek," according to Serrano, with administrators telling him to report each cheating case individually. "Ridiculous," in his view. He wants a stronger stance. "We cannot afford to have a society in which a significant fraction of our best young minds think that cheating is OK," he said. "That leads to a declining society, to a failed society … We cannot choose to become idiots." Further discussions are ongoing.

Better homework, worse exams

Serrano's case isn't unique. Two recent studies show the same thing: good homework grades, bad test scores. One study comes from central China. It tracked more than 26,000 students in grades 7 through 12 over 30 months. Six months after students started using AI, homework scores rose by 18 percent while completion time dropped from 64 to 45 minutes. Exam scores fell by 20 percent.

On entrance exams, the long-term loss ranged from 18 to 24 percent, with the full effect taking about two years to appear. About 81 percent of long-term users fit the pattern: faster homework completion, high homework grades, poor exam scores. Top students were hit hardest, losing 24 percent of their performance.

A UC Berkeley study covering more than 500,000 grades at a large Texas research university showed that in courses heavy on writing and programming assignments, the share of A grades jumped 13 percentage points after ChatGPT launched. The effect was concentrated in unsupervised homework. Courses with a heavy homework component saw an increase of 16 percentage points higher than courses that relied more on proctored exams.