You can also start the training with a simple water spray bottle and if you catch them starting to scratch where you do not want them to you give them a squirt - most cats hate that. Now I do have one cat - Fang my Maine Coon who seems to like getting a spray - so this does not work on him. I never hit my cats - it is instinct for them to scratch so do not ever hit a cat - it is just mean.
You need to provide them a place they can scratch that is allowed. You can visit my Squidoo page HERE to see all the great ways to train, all the fun available scratchers and even directions on how you can make your own.