A new study argues that a good amount of our adult personality is set by 1st grade. Here is some of the methodology of the study:
Using data from a 1960s study of approximately 2,400 ethnically diverse schoolchildren (grades 1 – 6) in Hawaii, researchers compared teacher personality ratings of the students with videotaped interviews of 144 of those individuals 40 years later.
They examined four personality attributes – talkativeness (called verbal fluency), adaptability (cope well with new situations), impulsiveness and self-minimizing behavior (essentially being humble to the point of minimizing one’s importance).
As the authors suggest, it would be interesting to see more research that explores how and when personalities might change.