Cob is a great technology to work with, unhurried. You can’t raise more than about a foot and a half of wall on any given day, because beyond that the self-weight of the mud will make it slump. And then you need at least a day, even under a fierce sun, to dry out the built wall sufficiently for the next build. If you have lot of volunteers however, there are two ways you can go.
A number of cob block bricks can be moulded in forms [this is actually the adobe route] and sun dried. These can be passed on by a line of volunteers and a greater height can be built in one day.It is useful to have a number of cob blacks handy anyway. There are many places they come in handy, like when fairing a detail, working at a height, making ledges or tiny lintels.
The second option is the one I followed when a group of over ten enthusiastic volunteers showed up one day. I had begun work on both the bath-space and the kitchen. So there was more length of wall to work on in two separate locations.