Rob

I generally use rolled oats. I place the dry oats in the bottom of the container add boiling water so they swell and go porridgy (but without having excess water on the surface). Once the oats have cooled I sprinkle on some bakers yeast and put in the microworm starter culture. You may need to mist with a little water at this stage if the mix is a little on dry side. As Bruce metioned it varies as to how long the culture lasts - I find that if production starts slowing down adding more yeast, more water (if it has started drying out) or both can get things moving again. If this doesn't work then it is time to start a new culture - providing there is still some movement in the old culture you can use a dollop from that to seed the new one.

A variation of the plant growing experiment I've seen is setting up identical plants but under different fluorescent lights (warm white, cool daylight, plant grow, etc) to see how much of a difference the different lighting made.  Best to choose a plant that normally grows quite quickly, so that you can get measurable results in the time available).