Hi Hannah,
Like you, I'm a complete novice at incubating and hatching, and I've got a dozen quail eggs in my little Brinsea Mini advance incubator at the moment, due to pip this weekend I hope. I just wondered if you'd come across two paperbacks I've found very helpful, which would also be good for the children in your class to use for researching your project, ie Katy Thear, Incubation; a guide to Hatching and Rearing see amazon http://www.amazon.co.uk/gp/product/090613725X/ref=as_li_qf_sp_asin_tl?ie=UTF8&tag=poultrykeep09-21&linkCode=as2&camp=1634&creative=6738&creativeASIN=090613725X (£3.34)
also Terry Beebe, 'Hatching and rearing your birds' see amazon http://www.amazon.co.uk/mn/search/?_encoding=UTF8&x=16&tag=poultrykeeperforum-21&linkCode=ur2&y=20&camp=1634&creative=19450&field-keywords=Hatching%20and%20rearing%20your%20birds&url=search-alias%3Dstripbooks (£9.99)
Both of these give a lot of clear information about what to do when setting up an incubator and also preparing the brooder for when the ducklings or chicks hatch. I'm finding this takes quite a lot of time and thought, when you're doing it for the first time. Our house is a bit like a maternity ward ATM! I've found that the temperature drops a lot at night, even in a centrally-heated house, and I expect that your classroom also has quite wide variations in temperature when the heating is switched off overnight and at weekends. Something else to think about and plan for, if you want to brood them for a few days in the classroom after hatching, though if you wait until after half-term, as Tim suggests, and then add on another 28 days to hatch, maybe it'll be a bit less cold by then.
There's also a thread running at the moment on here, about setting up and heating brooders, see http://poultrykeeperforum.com/viewtopic.php?f=30&t=3636 which i've found useful.
(Edit

Was there any particular reason for choosing to hatch ducklings rather than chickens? I don't know what you plan to do with them after they're hatched, but of course the incubation period for chickens is only 21 days, a week less than ducks, which might be helpful in your planning.