Goetz, T., Nett, U. E., Martiny, S. E., Hall, N. C., Pekrun, R., Dettmers, S., et al. (2012). Students' emotions during homework: Structures, self-concept antecedents, and achievement outcomes. Learning and Individual Differences, 22(2), 225-234. doi:10.1016/j.lindif.2011.04.006.