I trained mine before I let them out by banging on their dinner plate (a snack of fruit, oats, yogurt, cheese, whatever) every time I gave it to them, so that they recognized the sound. When I finally did let them out, they'd come running when I banged on the plate!
Recently they discovered the compost heap, however, and I actually had a couple chickens refuse to come in when I called. I had to chase them in. Then yesterday I forgot to count them when I shut them in, and woops, during dinner we looked out the window and saw a stray rhode island red casually pecking around on the patio. It's very unusual for one of my chickens to get separated from the flock (though sometimes two will) so I don't know how that happened.
I've considered just letting them come in on their own, but I'm nervous to leave the coop door open to all and sundry when it gets dark. I'm afraid a raccoon could sneak in just after sunset but before I get out to close up.