Well sort of, but the trainer is doing the selecting. For an example of one pokemon that gives an EV in each stat, look at the following:
HP...Bidoof (1 per)- it's the only one i know so far and it's really easy to find

Atk: Staraptor (3 per)- a few trainers have these; use the Vs. Seeker on the cyclist on cycling road that's at the first break in the paths.

Def: Graveler (2 per)- many caves have a lot of these, Iron Island worked best for me

Sp. Atk: Haunter (2 per)- the mansion in Eterna Forest is the only place I can think of right now

Sp. Def: Tentacruel (2 per)- look in the water, they're virtually everywhere.

Speed: Staravia (2 per)- very common, try the area north(east) of Valor Lakefront

More tips: go to the battle tower and get enough points to buy the braces, each one doubles EV's for a different stat

You didn't tell me about the Tentacruel thing, I looked it up.
And that IS how it works, and I know Wolves don't eat foxes, but I was half asleep, give me a break.
And ZIggy, your wrong.

Atk:
Gyrados - (Super Rod) Route 229 - 2 EV's, Encounter Rate: 100%
Kricketune - Route 212 North - 2 EV's, Encounter Rate: 60%

HP:
Wooper - 212 East (Surf) - 1 EV, Encounter Rate: 90%
Evolved Form of Wooper (Swampert? Probably not, I don't remember) Route 212 East (Surf) - 2 EV's, Encounter Rate: 10%

Def:
Geodude - Ruin Maniac Tunnel/Cave/Extension - 1 EV, Encounter Rates: 80%, 95%, 90%
Pelipper - Pokemon League and Route 224 (Surf) 2 EV's, Encounter Rate: 60%

Sp Atk:
Gastly - Old Chateu - 1 EV, Encounter Rate 100%
Golduck - Resort Area (Surf) 2 EV's, Encounter Rate 100%

Sp Def:
Tentacruel - Route 223 & Sunnyshore City (Surf) - 2 EV's, Encounter Rate 60%

Speed:
Fearow - Routes 225 & 226 Morning Only - 2 EV's, Encounter Rate: 60%
Poliwhirl - Routes 227 & 228 (Surf) - 2 EV's, Encounter Rate: 70%
Magikarp - Old Rod ANYWHERE - 1 EV, Encounter Rate: 110% (Your gunna get it EVERY time)

I read re-battling with certain previous trainers rises those stats more than battling ordinary pokemon.

Yeah, by a teensy bit. So far I've gotten one Poke to level 37 in one day. One's finally lv100!

I suggest just sticking with the list, it's easier and theres a MUCH lesser chance of messing up. Especially if you go for the 100% encounters.

Neyro: Do you mean the list you submitted? Is this the best locations in your opinion? I was going off of a guide from gamefaqs and it suggested by battling with trainers but when my pokemon levels up, he received no extra stats

Some kid on gamefaqs just said the stupidest thing I've ever heard: If they're level 100 how do you intend to give them movesets?

OMFG, it's called TMs dammit!

Yeah, I mean my list. I actually got it from a site that I trust a lot. Also, you won't really notice your pokemon getting the stats, it looks like it's leveling normally. Just you wait.
And in my opinion, it is the best locations.

What do you mean you wont notice the pokemon getting the stats? It doesn't show up when they level up? If not, than when does it show up?

It shows up at different points all the way to level 100. You won't notice it much, but the changes are happening.

Neyro, the other day you were trying to find a sp. def. EV pokemon and I told you Tentacruel (and your is possesive while you're is you are).
Next, using rods doesn't guarantee anything because sometimes, nothing shows up.
The trainer with Staraptors I referenced is more efficient than using rods to find Gyradoses and gets more EV's per battle.
On Iron Island, like I said, you will only find Graveler (2) and Onix (1) and the occasional Steelix (2) over 95% of the time (Golbats MIGHT show up but rarely).
About the Gastly in Old Chateu, there are also Haunters (2) and I think even Gengars (3).
About Tentacruel, I already said that, you didn't add anything there. About Staravia, use Pokeradar to help them show up more (especially in the Trophy Garden).
Magikarp only give you ONE and crap for exp. so they SUCK. And I think you should re-check Poliwhirl because it doesn't make sense.
About HP, why list something with an encounter rate of 10% (and it's Quagsire not Swampert)? And bidoof is nearly as common as Whooper.
Finally, do more of a background check on information before you criticize it.
***The number of EV's is in parentheses

You'll notice it if you compare stats at level 100 for that Pokemon to the average stats of a Pokemon at that leve. For more information go to:
http://www.smogon.com/dp/pokemon/

THe site I got the information from has been checked over millions of times, it's been there since Crystal. I just copied and pasted the information from there. You don't have to correct even tiny mistake I do, this isn't a college essay paper for gods sake.

Wow, Ziggy, you kinda went all out correcting someone... I think you should slow down a bit.

It kind of agitates me when somebody tells me I'm wrong and then uses info that I said as his own or use info that isn't as good in some cases.
But I did overdo it with correcting your grammar...

Anyway, this is getting a little off topic. Let's put the train back on the tracks. I've gotten one of my Pokemon to level 50.

I'm way behind on my training. I'm still trying to get some stuff off of Wifi, since I'm not having any luck.

Also, I didn't use any of the info that you told me, I used the info of a SITE. I just copied and pasted it's list. Also, I knew about the Tentacruel thing before you told me.

I'm busy as hell: Web design class, other classes, that damned essay contest that I have to get my ass moving on, a novel that I am so addicted to writing right now, Playing WoW, writing my stick comics, keeping up my blog/Youtube pages, and ultimately having a social life are just slightly getting in the way of my training of the Pokemons.

Yeah, but you had a mental lapse and forgot (or you wouldn't have asked me). You did repeat things that I already said, and I now have a level 55 Tyranitar with most of the stats that I wanted, but his Speed and Special Attack should be reversed.

I have a good Pokemon that has 360 HP and I can't wait to finally train my team more!

Yeah, I'm having trouble. Trying to breed a Modest Raichu. Thing's arn't goin well.