Harder to get clipped whites in PV2012 due to design (auto-recovery of highlights), but if you bump the whites slider you can clip more, then if not enough, you'll have to paint the rest (e.g. high exposure).
You may be able to use PV2010 to more readily achieve all-white background without painting, but note: your subjects hair won't look as nice around the periphery...
Note: max exposure around the outside edges will work just fine, but if you need to paint closer to the models, you can ease off the exposure, and crank highlights and/or contrast up instead, which will assure darker hair and such does not get over-exposed. Worth trying auto-mask too, although it doesn't always work so good.
I use Photoshop and Camera RAW quite a bit, everyday infact, but I have no idea what PV2012 or PV2010 is? Is it to do with Lightroom?
PV = Process Version, - applies to ACR too.
PV2012 is the current version, and PV2010 is a few years old now...
Check near the camera calibration section.
Yep - you have found it. I assumed (wrongly) you were using the most recent version of ACR.
Consider upgrading to v7.3.
If you continue with current version, then there will be no "whites" adjustment, nor brushable "highlights", but the rest of what I said previously still applies (paint with +exposure and/or +contrast to drive the stubborn parts of background the rest of the way to clipping.
Obviously (or not), the other option is to use Photoshop's other "pixel" masking tools, instead of Camera Raw.