I begin the year by doing a running record with each child to determine his/her reading level. I use the Rigby PM Benchmark Assessment kit.
Different companies use different leveling systems; the books in our book room are all leveled according to Fountas/Pennel. There are level correlation sites on the internet, so if I order from a company that doesn't use the F/P system, I can find the correlating F/P level.
After I have a reading level for each child, I put them in groups of six or fewer based on reading levels. The groups are flexible and change often throughout the year.
Each of my students has a browsing box. I found some great plastic baskets for 50 cents at a discount store. The kids put the books they've read in their guided reading groups in their browsing boxes; they read them for familiar reading at the beginning of their group and during silent reading time.
I've collected a good supply of single copies of books at various levels, so at the beginning of the year I give each student three or four books a couple levels below their instructional levels to start their browsing boxes.
Since you and another teacher will be in the classroom, I'd think you'd each take a group.
My district is very fortunate to have two parapros who are trained to do guided reading. Our Title teacher also takes a group, so there are four adults trained in guided reading (including myself) in my room for 30 minutes every day; each teacher takes one group.
We rotate groups every month. I have a 30 minute silent reading slot every day, so I can listen to each child read twice a week. I use information I glean from listening to children read, info provided by the teacher who's working with a group, and formal running records (every 9 weeks) to switch children to different groups or move a group to a new level.
When I started doing guided reading, I had to do all the groups myself; I had four groups. The groups didn't match exactly (for instance, I had one group that had kids at levels A and B, one with D and F, etc.), but I couldn't do more than four groups.
I scheduled an hour a day for guided reading and saw three groups a day for 20 mins. I saw the two lower groups every day, the next highest group M, W, F, and the lowest group Tues, Thurs. That was definitely not the best scenario, but at the time it was the best I could do...and it was a start
Students who weren't working with me read independently for 10 mins, partner read for 10 mins, and did a center for 20 mins. The kids who didn't have guided reading (because of being in a higher group) did two centers.
I spent a month teaching the kids how to do the centers before I started doing guided reading groups. I didn't have a teaching assistant or any parent volunteers to supervise/help with centers, so the kids had to be very independent.
If you'd like to know more about the centers I did, I'd be happy to share that information...please PM me if interested. I have some books at school that have been very helpful in developing the centers; I can share the titles with you, if you'd like.
Are you using a Guided Reading program (Wright Group, Rigby, etc.), or will you order books from various publishers? Just curious.
I hope this helps. I'm excited to read about how other teachers run their groups, centers, etc. This is a great place to learn and exchange ideas.