Duckworth's character lab (https://characterlab.org/resources/grit)
Duckworth, A.L., Gendler, T.S., & Gross, J. J. (2014). Self-control in school-age children. Educational Psychologist, 49, 199-217
Dweck, C.S. (1986). Motivational processes affect learning. American Psychologist, 41, 1040-1048.
Dweck, C.S. & Leggett, E.L. (1988). A social cognitive approach to motivation and personality. Psychological Review, 95, 256-273.