Hermann Ebbinghaus
In 1896, he did a test on children in school: The pupils had to complete sentences, and their teacher had to rate each pupil, if the pupil was in the lowest, the middle or the highest third of all the people in the class. Ebbinghaus saw a relationship between the teacher's rating, and the result of the pupil, but he could not give a correlation (because he was lacking the tools to do so). This was possibly the first test of verbal intelligence in a group.