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 play the role of the metric system, explaining to the US standard system how they're better.
Included is an example of a class brainstorming session that I completed with my 7th graders (this is their first RAFT of the year), to give you an idea of what that might look like, as well as an example RAFT, about a different science topic.
I typically score mine in this fashion:
Accurate and complete science content = 75%
Correct grammar/spelling = 20%
Proper format = 5%