Here's a little pop quiz.
Multiple-choice tests are useful because:
A: They're cheap to score.
B: They can be scored quickly.
C: They score without human bias.
D: All of the above.
It would take a computer about a nano-second to mark "D" as the correct answer. That's easy.
But now, machines are also grading students' essays. Computers are scoring long form answers on anything from the fall of the Roman Empire, to the pros and cons of government regulations.