easy cut flowers for school please???

Id like to grow some flowers in our school garden so that we can cut them for putting in staffroom and reception area. Ive grown sweet peas (with the beans),cosmos (pretty) and marigolds (OK and will reappear no doubt!), and last yr some more insect attractors -some of which were ok to cut.
Ideally something which low maintenance and in flower as early as poss- we finish 3rd week of July, then back 1st Sept (so we want some autumn flowers too-  Cosmos has done well).
We have 5 beds of (improved clay soil) quite busy with veg growing in rotation, so not a huge space. We've got a (very) cold plac greenhouse and quite a few willing (small) hands.  Any ideas gratefully received!

Thanks Yorkie! I love those Carol Klein progs... and Ill look up nicotiana too.  They do smell delicious (always a bonus).  Ive been cutting bits of an old viburnum so that we have some flowers in the reception area- but someone didnt like the smell!
Ive got asters in my own garden which are good in autumn so i could find another space at school to use for them -- good idea

Kaffir lily are good,I can't remember the latin name sorry.They flower from October onwards.Buy as bulbs as they are much cheaper.Nerines also flower in the autumn and are also better value as bulbs.
Remember to plant bulbs in the autmn for spring cut flowers daffodils,tulips,hyacinths etc etc.Alliums also make good cut flowers

Hardy chrysanthemums might be worth considering as some flower through to the end of October.

In all cases, if the children can get to the plants easily, take care with plants that are particularly harmful.

Someone fussed at my school when I wanted to plant fox gloves years ago 

Thanks Learner.. Ive been having a look at sources of chrysanths.  They could be a good option.. I could put some in the borders around the school building maybe.  It seems Id get small plants in April then grow them on ..? They are a bit tall at 1m ish maybe- but perhaps there are better dwarf ones?

And yes one has to be a bit careful about children and plants- but we've got some foxgloves i think.. we teach them to wash hands after being in the garden. I might be more concerned about plants with irritant sap, rather than poisonous berries...
Today I had 2 lads wielding sharp secateurs not particularly expertly- but they enjoyed it and its the only way to learn!

I couldn't agree more with you about children being taught to take care with plants rather than having all possible risks removed... they certainly wont learn that way.

Sources for chrysanthemums - Try Woolman's hardy spray varieties. Not sure how harsh the worst of your weather is but I moved mine to an unheated greenhouse fo the winter.

Lots of nice colours and great for picking!