Which type of assessment gathers samples of different work products over time?

Portfolio assessment is the correct choice because it specifically involves the systematic collection of student work over time, allowing for a comprehensive view of a learner's progress and achievements. This approach enables educators to evaluate not just the final outcome of a student's work but also the process and growth that occurred during the learning journey. By including various artifacts, such as drafts, projects, and reflections, a portfolio provides a multifaceted perspective on a student's development and skills.

Other types of assessments serve different purposes; for example, diagnostic assessments are typically used to identify a student's existing knowledge and skills before instruction begins, while formative assessments are ongoing checks of understanding during the learning process, allowing for immediate feedback and adjustments. Summative assessments are conducted at the end of an instructional period to evaluate what students have learned, often resulting in a single score or grade without the iterative nature of portfolio assessments.