Introduction: Students' perceptions of the assessment tasks can be a basis for optimizing the classroom assessment environment. In an attempt to quantify students' perceptions of assessment, Dorman and Knightley (2006) developed Perceptions of Assessment Tasks Inventory (PATI). This study sought to provide evidence for the construct validity of the PATI. Method: A descriptive research design was employed in this study. Using a cluster sampling process, the participants were 330 Omani students (175 females and 155 males) enrolled in grade 11 science classes. Three instruments were used in the study concerning self-efficacy, perceptions of classroom assessment environment, and perceptions of assessment tasks. Data were analyzed using confirmatory factor analysis, cluster analysis, multivariate analysis of variance, one-way analysis of variance, and Pearson product-moment correlation analysis. Results: Results indicated that a five-factor structure of the PATI provided a good fit to the observed data. Cluster analyses suggested three clusters of students who were distinct with regard to their perceptions of the assessment tasks. Scores of the PATI subscales correlated positively with perceived learning assessment environment and negatively with perceived performance assessment environment. The PATI scores had acceptable levels of internal consistency reliability. Conclusion: In conclusion, the results support the utility of the PATI for research and instructional purposes. It offers information that can be used by teachers to better orient classroom assessment toward improved student motivation and learning. Researchers might need to conduct studies linking between perceptions of assessment tasks and other characteristics of students and teachers.