Despite the number of studies investigating affective aspects of test taking, little is known about how students perceive the kinds of extended performance assessments currently being developed for state and local testing programs. This paper presents two studies that address these issues. In the first, hands-on science tasks were administered to 20 sixth-grade and 29 fifth-grade students who thought aloud as they performed each task and answered interview questions afterward. In the other study, mathematics items were administered in three formats (multiple choice, short-answer constructed response, and extended problems) to 29 high school students who were interviewed after completing the items in each format. Results of both studies indicate a great deal of variability in the affective responses of students to novel assessment formats, and they suggest some possible influences on these responses, including the importance of the nature of engagement and students' perceptions of validity and fairness. Three tables and one figure present study findings. (Contains 16 references.) (SLD)