Peer Assessments - Better than teacher assessments?

I love to watch TED Talks, and this one was quite a good one.



Daphne Koller speaks about Coursera, an online resource for taking actual credited courses.
She talks about the many advantages of this type of learning, particularly the fact that its free but one thing she touched on that I picked out was the Peer Assessment...

She speaks of the fact that each course could have somewhere around 100,000 students and the near impossible task of having one instructor grade every assignment that is submitted. The solution was to have (along with the computer assessed multiple choice and short answer questions) a peer assessment grading system.
The idea of peer assessment is not new, it has been done before but as a credited method of assessment? Not so much. And it make you wonder why.. Do we believe that the students are not 'qualified' to grade tests? Or might they be biased and 'go easy' on their peers? Not so sure.. In the talk Daphne references this paper by Philip Sadler and Eddie Good that shows a correlation of teacher grading and peer grading.

You can actually see that the correlation is very good. Students grade their peers similarly to teachers!

Personally I think this is an advantage as it also reinforces the learning the student who is marking (somewhat of a derivation of the 'teach to learn' concept) and also increases the confidence of that student as well. For the student being graded the advantage is they can have multiple grades, therefore multiple feedback from different perspectives which also enhances their learning experiences.

Some might think that this is a great idea for the post-secondary learning in Coursera, but could it be done for a younger audience? Funny enough though, the Sadler/Good paper referenced above was actually a study on middle school students! That is to say maybe 12-14 year olds are grading each other and giving grades similar to that of their teachers! Personally I think this is phenomenal. And I would challenge to consider incorporating this peer assessment into their teaching. The benefits for learners can be great and an added bonus is less marking for you!