This has been folded in to nearly every single other peer teaching post, but given how driven we’ve become by quantifiable assessment it deserved to have its own post.
The short response to this is, “Peer teaching is not quantifiable.” It’s not, but it is can be assessed qualitatively, and this is a good thing. It allows the teacher (or the person assessing) to determine where the student is in terms of which concepts have been learned and how well they’ve mastered the concepts. While peer teaching can happen outside the classroom, the peer teaching that happens inside the classroom rarely occurs in a bubble.
Let’s talk for a minute about the peer teaching that happens outside the classroom in service of what’s going on inside the classroom. It’s a long-standing tradition for struggling students who don’t feel comfortable asking the teacher or a tutor for help to approach a student they know understands the class for help. So, it may not be visible, but its impact is. I don’t advise asking the struggling student who they got help from; but an observant teacher will usually be able to determine it. (The teacher, observing a struggling student not asking for help, can also ask a student with a stronger grasp to step in and help the student.) The point here is that there are usually clues to suggest who the peer teacher is, and that allows the teacher to tacitly assess that student’s knowledge and application skills.
To assess students through peer teaching, you don’t even need to have the students directly engage in peer teaching. You can learn a lot about what the student understands and how well by watching how s/he organizes material related to the concept. The newbie doesn’t know yet what’s important or how ideas relate to each other, and so s/he saves everything in a manner that often has little more than a surface organization structure to it. The expert (or more advanced student), on the other hand, has learned what’s pertinent (or how to sniff out the important information) and organizes it in a relational manner that allows for better access and retrieval.
This is where having students curate their learning journeys is helpful because you can see what they save and how they save it, and this gives you a pretty clear picture of where they are in their learning journeys. (There are exceptions to this. I was a cataloger/archivist-in-training from a young age, and as a result would not invite a teacher to judge me based on my collection of information. My organization of it? Sure. But not the mass of information I had stored at any given point in time. Just a word to the wise on this one. Although…I can see where you might be able to distinguish between the inexperienced, the packrat, and the completionist here.)
In the fight to make the long mythical authentic assessment a reality, peer teaching offers a lot of potential as a real and diverse set of tools to determine where students are in their learning.