At our school we have hall seating for 200 kids, and 450 kids to get through lunch....
We run a rolling lunchbreak - mixed hot dinners/packed lunches so the kids can sit with their friends -
all of KS1 come into the hall at start of lunch, then when there are around 30 spare places, we call in the next class from the playground - we get through them all in the hour - with ruthless efficiency 
slow eaters (mainly reception - the others have learned to eat quicker or bring less) sit on the row we clean up last - since the hour also has to include cleaning the hall and putting away 24 tables , 40 benches and the mobile hot food serving unit ready for afternoon assembly or PE.
We midday supervisors feel like we have earned our £6.75 by the end of it! since we are also cleaning up as we go, watching for choking, clearing up various bodily fluids, doing first aid, chopping up hot dinners, opening 20 stick yoghurts, 12 babybels,
arghhhhh innocent smoothies - don't get me started on those....
2 mandarins from the bottom of the fruit bowl, 3 lunchboxes that the child can't open, finding a teaspoon for the teeny petit filous, watching kids in playground if it is our turn to go out, doing even more first aid, watching to see no one is being excluded, dealing with petty - but important to the kids - squabbles, making sure everyone has their coat on - doing up 26 zips, putting on 30 pairs of gloves (and in reverse when the cold air means they all need to go to the loo urgently) chasing the older ones out of the toilets - what is the fascination with chatting in the stinkiest room of the school, and getting them to line up after playtime.