Intellegence tests are a good form of placing where we are in education. For instance, we take placement exams for college. Without these tests we may be put in classes that are too easy or too hard for us based on our intellegence.

Placement testing also helps at the elementary, junior high, and high school levels. We test for gifted students so that they will not be in a class too easy for them. If they are in a class where their mind is not engaged, they will be bored and therefore disruptive. This in turn affects the other students in the class.

1} We have found that as far back as the mid 1600's students were taking informal placement exams for Latin at Harvard. By the end of 19th century, colleges and universities everywhere had implemented placement testing as requirements.

Of course, we must also take into account that not every question has an informed answer and some test takers will just be guessing. This does skew the resutls somewhat, but as a whole, test taking seems to be the best model to use when choosing what classes we should be taking. 

Sources:

1}w​ww.wikipedia.com