I settled on these four:
Facilitator - This person makes sure that everyone understands what's going on and what they're supposed to be doing.
Resource Manager - In charge of the materials.
Process Recorder - Keeps track of how the group made decisions or arrived at conclusions.
Skeptic - Looks for alternate explanations, things that might have gone wrong, or things the group might have missed.
The Facilitator is common so I'll skip that explanation.
I have a spot on my board for the Pre-Flight Checklist (Do Now) and materials. The checklist shows the things a student does right away along with the time they have to complete it. Usually it's three or four steps with stuff like answer the question on the board, open your notebook to page 58, process your notes from yesterday, finish the writeup from yesterday, etc. I used to just start with a question every morning but I found that to be too limiting. I like the comfortable routine of knowing what to do when you come in, but I don't need them to, for example, copy down a learning goal every single day. This gives me a little more flexibility while still maintaining some structure.
The materials section lists what students should have out immediately like notebook or portfolio. There's an additional section specifically for the Resource Manager. He or she gets the whiteboard markers, scissors, colored pencils, etc right away but doesn't distribute them until instructed. They get and put away lab materials when it is time and turn in papers. At the end of the period, the Resource Manager supervises cleanup.
The Process Recorder is new. My goal is to have this person record the discussions and decisions of the group. Why did the group make this decision? What particular piece of evidence led to the group's conclusion? I also wanted the disagreements and dissenters to be recorded.
The Skeptic originally started as the Double Checker but I decided that wasn't interesting enough a job. Their job is to make sure the group ruled out other explanations and to make sure the group isn't missing anything important. In my perfect scenario, the group would end up needing to devise an alternate or modified experiment based on something the Skeptic noticed. I'm not sure I have the ability to help them get to that point on a regular basis but you can bet I'm making it a BFD whenever it does happen.
Especially at the beginning, I give sentence frames and question cards to guide them as they're working. The Facilitator and Skeptic will turn in a brief report. The Process Recorder will submit an annotated procedure.
Here is the handout I give them. They paste it into their science notebooks.
Luann Lee posted hers here and has a whole bunch of different ones if you're looking for some variety.
Other odds and ends:
I number (not physically) the seats at the tables like this:
When we go to rows then I use A/B partners but usually we're in tables of four. I rotate jobs on a week to three week schedule depending on what's going on. I use a poster to keep track and the same numbers will have the same role. It's nice because you can quickly determine who is supposed to be doing what. The numbering/letters work well for lots of other stuff as well. "3s go to station 2." "Bs will go first." "Odds start with the timers."
PS - I forgot to include this in my classroom management post for noobs. If you're a science teacher buy a multi-tool and carry it around with you. I have a Leatherman Juice S2 I got from Target. You have no idea how often you'll be doing quick fixes of various lab equipment in the middle of a period. Also take a look at your desks and chairs and see what you'll need to tighten them up. I've got a folding hex key set that can fit my random assortment. You ed program probably didn't mention how much of your time is spent fixing stuff.
PPS - If you run an ed program, "equipment maintenance and upkeep" would be an excellent class for science teachers. I have no idea what I'm doing most of the time. If it's not a dead battery or a loose screw I'm SOL.