I work in a small school (60+ pupils) and I'm thinking of suggesting that we run activities for vertical groups of children for about 45 minutes on a Friday afternoon, to foster a sense of community and cooperation.
I've participated in this as a supply teacher and I thought it was a lovely way of bringing the children together.
I'm envisaging four vertical groups (so a mix of pupils from P1 to P7, about 16 per group), going with a different teacher each week. Each teacher would do a different type of activity, repeated over four weeks until she had had every group.
I thought one teacher could do something sporty in the gym hall, another something arty/crafty.
Sounds great. I developed a similar idea (in special school - very mixed ages) with the aim of teaching particular communication skills. Students chose their half termly activity from a selection - anything from junk modelling to gardening to parachute games - and all had a couple of communication targets to work on during that activity. Perhaps in mainstream you could have social skills or learning skills targets to cover. Or preferably, you wouldn't need anything like that, as the purpose of the activity is obvious! But for convincing heads/ timetabling and subject coverage maybe you'd need it.