Hi Megan,
We have done this in the last three years. For context this was done as our school in the last seven years had doubled in size, so adding two more houses from four to six was needed as our House system also supports the Pastoral Care structure in Years 9-12. Major steps we took:
1. Naming – Straight forward, we are Anglican and our Houses are named after Saints, we had four male Saints so being co-ed we immediately moved to adding two female Saints, which meant our options were limited by the small number of female Saints recognised by the Anglican Church (as opposed to Catholic Church).
2. Colours – House colours came from an association with the new Saints
3. All students in Years 5-12 could opt in to one of the new Houses, we had a good response (it highlighted that some students didn’t like their current House Leaders, who they expected to be the Leaders in the future, some of the staff involved in those Houses or their Pastoral Leader in Senior School).
4. We didn’t conscript anyone, but instead added new families that entered the School more into the new houses, keeping an eye on numbers and balance
5. We moved any Sporting/Co-curric event that had a House point allocation to a handicap system for a period of three years until the numbers were more evenly matched.
Hope this helps in some small way.