The concept of mindsets describes the beliefs individuals hold about the innateness of intelligence. Although the theories of mindsets have received much attention in the fields of psychology and education, they have only recently gained interest among researchers of second language acquisition. In this study, the author investigated how praising some students for their success in tasks affected the performance of other students in the same classroom who were unsuccessful in those tasks and thus not praised. The researcher used possible and impossible crossword puzzles as an intervention to prime a fixed mindset in half of the sample. The average time to complete a crossword puzzle at the pretest was compared to that of the same puzzle at the posttest. The students who were given possible crossword puzzles and praised during the intervention were able to make significant improvements in the speed they could complete the puzzle at the posttest stage. However, such significant improvements in performance were not seen among the students who had been given impossible crossword puzzles and not being praised during the intervention. Possible reasons for these results and pedagogical implications related to types of praise in the classroom and testing will be discussed.