This test will winnow out the students who study from those who don't bother.
Also ahead: Some further winnowing of the field as trailing contenders decide whether to pack it in.
The Iowa results should help winnow what has been a sprawling and chaotic Republican field.
Iowa is traditionally a battleground for very conservative candidates, while New Hampshire serves to winnow the establishment side of the field.
With Iowas results banked, the GOPs historically large field could begin to winnow.