At the beginning of the year, each child's laminated name is placed in a colourful, attractive box. If I need people to do a job, a name can be picked; if I need people to answer questions, again a name is picked.  All children know they will be asked a question in Mental Maths, because they see the Blue Box there ready.  I pick partners/groups out of it for work in the ICT Suite, or mixed ability group tasks in other areas. 

It's very useful, as children see it as a 'random' method of picking (which it almost always is...); it worked very well with children who found taking it in turns difficult, because they knew their name was in there, so learnt that eventually they would be picked out.  Children can also pick their own partners from the box (then it's their fault, not mine!). 

The children in my class are very used to this method of being organised, and do not fuss about who they work with anymore - it's almost always guaranteed to be different the next time their name's picked from the box.  Also useful for when supply teachers are in that don't know the children's names.