How do you EV train in pokemon black and white?

Alright so i understand the process for the most part. everyone is assigned evs and by killing them u collect the evs. it takes 4 evs to equal 1 stat. so heres wat i do. i breed untill i have the pokemon i want at lvl 1, an aaron for instants. then i give him the power item that gives him 4 extra attack evs for every battle. he also has pokerus. so i fight a butt load of patrats but there seems to be no influence on my attack stat on my lvl ups. they just seem to lvl up normally. am i doing sumthing wrong?