In a recent interview with Japan’s Nintendo Dream magazine, Game Freak discussed improvements being to Pokémon X and Pokémon Y over previous games in the series. Chief among these is how experience points are gained during battle.
In Pokémon X and Pokémon Y, your Pokémon gain experience even when the opposing wild Pokémon is caught, according to a summary of the interview on Bulbagarden. Caught Pokémon will give the same amount of EXP as defeated Pokémon.
Additionally, the item Exp. Share will provide experience to all Pokémon in the party, not just the one that participated in battle. The participating Pokémon will receive 100% of the total EXP, while non-participating Pokémon will receive 50% each.