Experiments examined school children from the ages of 8 to 12. These children needed to plan out a desired academic future.
The control groups imagined only the academic future they wanted. They did not address how to reach that goal.
The study found that students with a plan reached their desired goal better.
Citation: Gabriele Oettingen, Gaby Honig, Peter M. Gollwitzer “Effective Self-Regulation of Goal Attainment” International Journal of Educational Research 33(7):705-732 · December 2000