Our chickens do fly. They definitely prefer to just run around but if one ends up far away from the flock they'll fly over to hang with their buddies. When our rooster gets away he'll fly when chased -- once I was chasing him through the woods and upon reaching a clearing he flew up about 15 feet high for...maybe 50 feet or so? Definitely far more than a 1 foot tall animal can jump.
I think they figured this out around 16 weeks old; Pig (aptly named) attempted to fly from their brooder box to the kitchen table because we were eating pork chops and she wanted more.