A large pot of water for everyones to throw their pence/small change in towards school funds, Weather station, Sand pit play area, Scree garden, Bog garden, Veg patch, Water feature, One statement piece stood in coloured glass, Hanging basket stand, Grass in a pot,
collection of pots, Wheelie bin stand, compost bin, water butt, One nice chair?
Lots you can do in 1metre. Lastly how about a stand with photos, map and history of the school in a waterproof material?

how about a mini veg garden for quick growing things like lettuce, radish etc or a smelly herb garden, as to Drc's statement piece have the art class make one every year