Pre Algebra Course Mastery and Course Mastery due date

Hello,

I am a middle school math teacher and have been using Khan Academy with my students since the start of the school year. 

I have a couple of questions about Course Mastery Placement and Progress. Specifically, I want to know exactly how the Pre Algebra course mastery works. I assigned Pre Algebra as a goal last semester for one of my classes, but when I go to the Placement tab it only shows 6^th grade and 7^th grade as course mastery goals. I assume this means the Pre Algebra course is made of parts from both those grades, but I want to be sure.

Also, I am hoping to have students work on the same course this semester. Can I edit the goals from last semester and change the due date? Will it save their progress and allow them to continue working from where they ended up in December?

Thank you.