A RAFT is a short writing assignment where students take on a ROLE, address a certain AUDIENCE, in a particular FORMAT, about a given TOPIC.
For my science class, since my focus is on the SCIENCE, rather than the writing, I keep the format simple...a letter.
In this RAFT, students choose from two different choices. In one, they write about a scenario involving a fleece jacket and a sock in the dryer (why they stick), and in the other, they write about why the metal bolts on a plastic slide will shock the rear end of the person about to slide down.
Included is an example of a class brainstorming session that should give you an idea of what that might look like, as well as an example RAFT, about a different science topic, so you can see how a RAFT comes together.
I typically score mine in this fashion:
Accurate and complete science content = 75%
Correct grammar/spelling = 20%
Proper format = 5%