It depends on numerous factors how EV training goes
1 - Does your nature support the stat your trying to boost?
If it doesn't the stat won't go up much no matter what.
2 - Is it a stat the pokemon is good in?
You say it is a Shieldon which means if you aren't training it in defence and special defence EVs it won't gain much any way
3 - What form is it?
Shieldon is pre-evolved so its stats are lower than Bastiodons so thus it won't go up as much. Don't toss aside all 510EVs until it evolves.
4 - Does the band support the stat?
Each band will only support only stat. Make sure it is the one matching the stat your trying to boost.
It all depends on who you use, what stat you pick, what EVs the target support, and the item your pokemon holds. I had a Regigigas level up once and gain 37 points in attack because of EVs, the proper band, a good nature, pokerus, and spamming Bibarrels and Machokes.
It takes time to adjust things properly and even then you may not get much out of it. The base and max stat of a pokemon is a key factor to how much you'll benefit from the EVs. For Shieldon try out the Oreberg Mines and Iron Mountain.