So you know how Neville was really bad at Magic for the first 5 books? And then he started to be good when he pushed himself in the DA.
But then he actually becomes pretty great from HBP on.
Well, in OtP he mentions that his grandmother would kill him for breaking his dad's wand.
The wand was his dad's.
Not his.
The wand chooses the wizard.
The reason he wasn't as good as he could be was because the wand didn't choose him.
Then he got his own from Ollivander's and he became pretty good.
Neville was ALWAYS a good wizard. It was just his wand.