An assessment is a premium feature. It is a test with no due date meant to gather information on a student's current status with their math skills. You select the grade and math subject, and the student will receive questions from that grade's skill levels, skills from one grade below, and skills from one grade higher. The assessment scores are not added to the student's overall grade, and the student cannot see their score, only the teacher can. The purpose of the assessment is for the teacher to have an understanding of the student's skill level so they can create the best study plan for the student.
An assignment is a free feature and works as either classwork or homework. It has a due date and the student will know their score immediately. The score is also added to the student's overall grade.