[Gill Catton]

The difficulty with reproducing a pond type ecosystem in a tank is that most members of a pond community leave it at some point - water boatman fly, newts and frogs are only there for breeding, dragonflies hatch and fly away etc......
you could possibly keep some stickleback or some frogspawn and let children watch it mature but I think most if not all of the interesting animals of a pond will only stay put and survive in a pond.

I keep tropical fish and have wondered on a number of occasions about keeping a native british set up but have repeatedly concluded that fish and snails and possibly flatworms are my only options! However stickleback are pretty and have interesting breeding habits (though they can be quite territorial so limit the number of fish) so they might be worth considering. Especially as in an actual wildlife pond - unless it's very big, I'd recommend leaving the stickleback out as they will eat most of the more interesting invertebrates and may deter breeding newts or frogs. I've lost count now of the number of wildlife ponds I've come across stuffed full of fish! It seems to be something human beings have evolved to have - a strong drive to put fish in ponds.
but anyway good luck with your project there are a multitude of options - quite excting!
If you're anywhere near Slimbridge, they have a very good pond dipping and information area for kids last time I went, - if you are after inspiration it might be worth a visit!