Converting Ac to DC is the most generic way to describe this, as Sophie points out it can be done with one Diode, from there the systems become more and more complex, each method had it's own benefits, drawbacks and pittfals - while this can be studied on paper ( internet - etc) - but IMO building each type will have the best impact.
I would start with a small step down transformer as an ac source ( get an adviser to help and make this to be safe), and build into a small experimenters box. 120VAC to 12-0-12 Secondary. This will provide 12V or 24V AC source. ( On the AC side, you will need the plug, a fuse, and a properly rated switch), bring the 3 low voltage leads to binding posts.
From this you can build rectifier circuits with the 1, 2, 4 Diodes, and experiment with different filtering etc. on a basic breadboard.
Some type of basic oscilloscope will be best to see what is going on - a PC one will, do but the inputs need to be limited to ?? 0.7V? - I am not sure, but you can build a basic voltage divider probe 100/1 to keep the ratios in check. I would also advise to "build" each circuit in Spice ( LTSpice is free) - before you build the real circuit - then compare the Spice results with your real world results.
A set up like this could support about 20-40 AC/DC conversion experiments. I have been thinking of developing this as a web-curriculum, but I would reference a suppler like radio shack for parts ( as I am based in the USA) -the Safety aspect of the AC supply is my biggest concern.
