Exams and portfolios measure different levels of student progress over specific periods of time. In a traditional exam, the student's performance is determined by one class period on one day. By contrast, a portfolio measures a much wider time period, as students often include multiple drafts of essays or their body of work composed over the course of a semester. While success on an exam depends on how much a student studies and comprehends the material, portfolios focus on the overall learning progress a student makes and the effort they put into the project.
A major difference between the two assessments is that portfolios allow for direct input from students. In a traditional exam, the student's ability to answer the questions correctly is the only factor that speaks for him. However, portfolios often require a self-evaluation component, such as a reflective essay, that lets students describe their overall experience in the class and the portfolio creation process. University of New Mexico professor Julia Scherba de Valenzuela writes that an advantage of self-evaluation is that it lets students practice critical thinking, letting them decide how well the portfolio measures up to course goals and standards.
Exams and portfolios also differ in degrees of student ownership. Because every student takes the same test and is judged according to correct and incorrect answers, traditional exams let them play a very small role in their evaluation. However, portfolio evaluation gets both students and teachers involved in the process. According to Multnomah Education Service District assessment specialist F. Lee Paulson, portfolios let students take ownership of their evaluation by showcasing their struggles and accomplishments and enabling communication with the teacher in a way traditional exams don't allow for.
Teachers ultimately use two different grading methods to score tests and portfolios. Traditional exams are more convenient to grade overall, as they involve marking incorrect answers and calculating a numerical grade. Portfolios, however, require teachers to establish their own specific grading criteria. Even after they determine this grading scale, it still may be hard to maintain objectivity, since the students' reflections and perspectives are part of the evaluation. Grading portfolios is also much more time consuming; teachers must not only read the students' work, but write comments explaining and justifying their evaluation.