This quasi-experimental study reports on the effectiveness of three assessment strategies for students' performance. The primary goal was to determine whether there are any improvements in students' conceptual learning when a frequent (weekly) quiz is used for grading purposes compared to using midterm and final examinations only. Another goal was to ascertain whether students perform better when they are allowed to work collaboratively on quizzes compared to students taking quizzes individually. The results showed that when the quizzes are open-book, and students have a chance to collaborate (discuss in pairs how to answer the quiz questions), they perform significantly higher in their final examinations and their final projects (an indicator of conceptual learning).