An example of an alternative form of assessment is a portfolio assessment, in which the work of students is collected over time such as projects, writing samples, reflections, and drafts, in order to demonstrate progress, knowledge, and skill acquisition. Unlike the one-time tests, portfolios can represent how learning evolves. For this reason, it is useful in assessing critical thinking, creativity, and application to real-life situations. Their strengths include offering holistic pictures of student growth and promoting self-reflection. They reduce test anxiety and support differentiated learning. Yet, they have weaknesses: they are time-consuming to review; without clear rubrics, they are challenging to grade consistently, and hard to compare among students or even classes. Portfolio assessment is a valid, learner-centered method of documenting authentic learning.