Snakes and Ladders game for Year 7 to introduce ideas of factors that affect population numbers. Just download and laminate a snakes and ladders board e.g. from http://www.printableboardgames.net/preview/Snakes_and_Ladders, then students play the game as normal. The only difference is that when they land on a snake or ladder they take a 'snake' or 'ladder' card and read out the cause of their good or bad fortune ie. a reason why their population has increased or decreased. To be honest, I've rushed it a bit so I'm sure someone could adapt it. It could also be adapted for older years; they could come up with their own reasons for population changes.