I taught for a short while in a one teacher school (since closed) with 9 students from K-6. I loved it.

Reading: Levelled at where they are at. Two kids may be at the same level but in different grades - go with it. I'd run this exactly as I would reading groups in a normal classroom.

Writing: Same topic, different expectations. You can't recycle topics every year, or the kids will catch you. I find

http://www.pobble365.com/ excellent for writing tasks. They have a picture and set of activities every day, but I find one easily lasts a week.

Maths: Work in the same area - so all groups might be doing multiplication, but at the different levels dictated by where they are up to. Work with each group intensively, and have other groups working on independent tasks within the area being studied. Have centres and explorations and challenge activities.

I did a lot independent work and made the kids responsible for their own learning. The higher grades (3-6) in my school had a "menu" of tasks they had to accomplish each morning, while I worked more intensively with the little ones. Then I would pull the bigger ones in for a lesson, and a check of their work while the little ones worked independently. I loved it.