Polygons are rendered as smooth colors instead of solid

I'm trying to render low polygon version of a model that I downloaded. Show in the image are two models, on the left is a low polygon model that I drew myself, the other is a high polygon model that I've used decimate modifier on the torso

I'm trying to achieve a "low polygon" look (like the model on the left), but when I view the model on the right those polygons appear not as solid colours, instead some smoothing looks like is happening. Is there a property that is controlling this somewhere?

In the Tools panels T under Shading you can toggle between Flat and Smooth.