Which of the following counts as a formative assessment?

Formative assessment is an ongoing process that provides instructional feedback to teachers and students about the learning progress during the instructional period. A teacher's observation of student progress exemplifies formative assessment because it allows educators to monitor students’ understanding and skills in real-time and to adjust their teaching strategies accordingly. This approach focuses on providing feedback to support student learning, rather than measuring performance against a fixed standard.

The other choices are not aligned with the principles of formative assessment, as they typically serve as summative assessments. A unit test evaluates what students have learned at the end of a unit rather than providing ongoing feedback. A standardized test is designed to measure student performance across a broad population and usually serves to compare performance against a national benchmark rather than its immediate application to instructing students. A final exam assesses students' knowledge cumulatively at the end of a course, which does not provide the same level of ongoing feedback necessary for formative assessment.