The model that we advocate at Creative Blogs has been developed over 12 years worth of experience of blogging with schools. Each class has its own blog and every child in the class has their own login. The teachers and TAs in each class monitor, moderate and facilitate the blogging. This distributed model promotes ownership by both adults and children alike and when used successfully has repeatedly been shown to have real impact on children's writing.
The main issue with the model is one of management. Each year end requires you to set up a new set of class blogs and to move the children and teachers from blog to blog. In practice, providing you are organised and work systematically the process will take around half a day.
To facilitate the update process we always run a series of courses to take you through the various steps needed (we're just finalising dates for 2016 now). Or, you can book us to come in to school to do it for you, at a cost.
However, if you are feeling confident and want to give the update a go yourself we have developed a step by step tutorial which we edit and extend every year. Here's a link to the notes: