Turning in to a 3 page essay is gonna take alot of imagination, you could go in to details about gambling theory and what exactly is considerd gambling in your introduction, go over things like the long run, short run, expected value, then you can maybe write half a page about luck and certian luck myths, check out
http://en.wikipedia.org/wiki/Gambler%27s_Fallacy then you can expmain the different aspects of skills, for example, how emtions play a large part of the game and bankroll issues, table selection, how the game is constantly evolving and how your skill can turn in to a handicap if you play too much of a mechanical game where people can guess your cards.
I would broaden your topic from just "luck vs skill" to The essentials to become a good poker player, and just include the luck aspect as a sub-category.