Can Duolingo Crush the TOEFL?

The test is broken down into four types of exercises: vocabulary (picking out real words from a list of fake words), cloze passages (completing sentences with missing words), listening (transcribing a spoken text), and "speaking" (reciting a written prompt). Settles points to research indicating that many of these tasks are "highly predictive of overall language ability"--people who perform well on them tend to be proficient users of English. Some sentences are culled from novels, news articles, or encyclopedias in the public domain. Settles and his team spent a lot of time designing natural language–processing algorithms that could read through the giant corpus of texts available online, automatically create appropriate test items, and then calibrate their difficulty. Because the test is "computer-adaptive," it becomes harder or easier as you give right or wrong answers, allowing your English level to be quickly pinpointed.