I don't think 100% accuracy is logically possible. Because it's entirely possible that someone would just naturally write the exact same thing as an LLM would write. And after the fact there is no way to distinguish the two. But pangram does have an extremely low false positive rate, which I think does make it useful for detecting cheating students. Assuming the base rate of cheating students is 1%, and assuming pangram has a false positive rate of 1 in 10,000 and a true positive rate of 7,000 in 10,000, that means ~98% of students flagged by pangram actually cheated. Combined with a teacher's familiarity with that student's previous work, which should rule out many more false positives, it should be a very useful tool.