This rubric can be used to hold students accountable during group work. It is in .docx form and can be adapted for your needs.
The rubric is simple and written in student-friendly language. It asks the students to grade themselves first, and then the second section is for the teacher to fill out. You can delete the top or bottom portion if you just want the teacher to fill it out, or just the students.
The rubric could be used for juniors and seniors, but might need to be adapted if you think your group of students will find it too juvenile.
I recommend handing the rubric out before the group activity so students know what is expected of them during the activity.