Flexibility in assessment is usually achieved by giving students choice over the assessment weighting, type or format, the timing, the criteria, or the overall assessment result. This study, however, demonstrates the development of a flexible assessment regime where students were given the choice to invest in within-semester tasks designed to encourage the development of higher order thinking skills. This was accomplished by incorporating two compulsory summative assessments and two optional tasks focused on the process of learning. Students could choose whether to invest extra time to complete all four tasks, or to concentrate their effort only on the compulsory assessments. Evaluation of the flexible assessment regime was conducted using a survey incorporating quantitative and qualitative questions. The data showed that students came to value the flexible assessment regime by the end of the semester. Qualitative responses indicated students thought they had developed their higher order thinking skills, but were unaware of how these skills were of benefit in their disciplinary context. A follow-up interview study was conducted to further understand students' responses. These discussions indicated that students thought the assessment options allowed them to scaffold their learning throughout the semester, reduced overall student stress, and encouraged the development of higher order thinking skills. This study therefore demonstrates that flexibility in assessment allows students to take a proactive role in their learning. When combined with activities designed to develop critical thinking, this assessment strategy can be effective in developing higher order thinking skills.