At the top of your screen, you'll see a link to your "Results" page. This page will include your scores from all past assignments.
You can access details about past assignments from the "Results" page.
On your "Home" page, you will see how many topics you've mastered this year and all time.
On the "Practice" page, a green star shows that you've mastered the topic in previous years.
Please note that if you leave a class, you will lose access to your old assignment and quiz scores. You will not, however, lose any of your mastery data.