There are two main reasons we are including pretests and posttests in our courses. The first reason is to measure student growth throughout the year. We want to equip teachers with the quantitative data to show that students are learning and growing as a result of their computer science courses. Comparing student performance on the pretest and posttest is a good way to measure student outcomes and demonstrate the importance of offering computer science at your school.
The second reason CodeHS is including a pretest at the beginning of the year is to give you data to inform instruction throughout the year. Ideally, students will enter your computer science course with strong math and logical thinking skills, but we know that sometimes students do not have a strong grasp on all of the prerequisite knowledge for a course. By giving students a pretest, we hope to help you identify potential stumbling blocks early in the year, so you can modify instruction to spend more time working on the skills your students need.