I think this skill is best described near the end of Chapter 1 of le Carré's Tinker, Tailor, Soldier, Spy, describing Jim Prideaux:
> He was also credited, despite his taste for tolerance, with a sound > understanding of the criminal mind. There were several examples of > this, but the most telling occurred a few days before the end of term, > when Spikely discovered in Jim's waste-basket a draft of the next > day's examination paper, and rented it to candidates at five new pence > a time. Several boys paid their shilling and spent an agonised night > memorising answers by torchlight in their dormitories. But when the > exam came round Jim presented a quite different paper. >
In the age of the Internet, this skill is very important for instructors to cultivate. Of course, it is much easier now — no waste basket required. It might be termed "reverse fishing".'You can look at this one for nothing,' he bellowed as he sat down.