When they were still on the farm we worked on the floor inside the barn. We were separated from other chickens by a wire and carton barrier (the could not see each other but they could hear us and us them). With more motivated and curious chickens it didn't take long for them to adapt and connect clicker with food (first they had to get used to eating out of a cup, the more frightened chickens needed WEEKS for just that small step). Once I took 3 of them home we started working outside on grass. It's a bit distracting for them (grass is still a new thing to my ladies) but they can work just fine.

My ZOO chickens also work on the ground (no chance of working on a table there!). With my next training project (handling feet) we're going to work on a table.
I already had my chickens walk all over the table (covered so it's not slippery!) to explore and get comfortable on it.
I used a target stick (the same one I use for training my dogs) - pecking it, as their first CT behavior. I added following, once they were comfortable with pecking it at different heights and in different positions. Some of them were afraid of the target at first so I gave them food and slowly moved the target close to them. Only if they were eating did I move the target closer, until it was all the way in the feeding cup and they were eating by pecking around the target.
A very bad quality video from a training session with one of my chickens back at the farm
https://www.dropbox.com/s/3kvla59g0gkppoj/SK Cr 4 polkrogle 3 test.wmv
I'll definitely make a new video sometime in the future with the chickens showing off what they know. I just need to borrow a camera and someone to hold it.
What are you using as treats? I'm using live mealworms with my ZOO chickens (I have fresh supply there) and a mixture of different seeds, their regular food mix and grated cheese for my home chickens (I haven't set up my own mealworm 'production' at home yet and they don't like eating whole corn).