  We develop a methodology to test the accuracy of lattice extrapolations of
the form factors in B decays only using experimental data. We test this
methodology by comparing the BGL parameterization proposed by Boyd, Grinstein,
and Lebed (1996) and the BCL parameterization proposed by Bourrely Caprini and
Lellouch (2008) in the context of $B \rightarrow \pi \ell \nu$. Our results
suggest that the BCL parameterization is a slightly better predictor of the low
$q^2$ region than the BGL parameterization and that this methodology can be
extended to other decays such as $B\rightarrow D\ell \nu$.
