You can assess student's homework/assignment by team, choose the reviewer from members in classroom (Teacher and TA role). Students will get the average scores and the reviewer will not able to know the score from other reviewers. You can manage team assessment as follows:
[[1.]] Click on the activity that you want to assess by the team.
[[2.]] Click Manage Reviewer to manage reviewer for students
[[3.]] Click Add reviewer for adding reviewer to the student (You can choose reviewer as much as you want and the score will be averaged)
[[4.]] Click Reviewer Name and then Save.
You cannot change status team-assessment if the assignment had been checked by reviewer. If you want to change, you need to create a new activity and students resend all homework/assignment again.