The Algebra 1 section on Khan Academy is broken down into subunits (Algebra foundations, solving equations & inequalities, working with units, etc.). You can see these subunits when you navigate to the course on Khan Academy. Each subunit will show how close your student is to achieving mastery in that subunit (look out for "x/x Mastery points" with a progress bar near the subunits' name). If you navigate to the Algebra 1 course homepage, you can also see a course summary on the left-hand side of the page which details all progress your student has made. 

There are no formal criteria for "passing" units on Khan Academy; you will need to discuss with your school's advisors what they consider acceptable to recover credit.