  The experimentally measured rates of the semileptonic decays K -> pi l nu and
D -> K(pi) l nu can be combined with lattice calculations of the associated
form factors to precisely extract the CKM matrix elements |V_{us}| and
|V_{cs(d)}|. We report on the status of form factor calculations with Fermilab
charm quarks and staggered light quarks on the 2+1 flavor asqtad staggered MILC
ensembles. Analysis of data for the D -> pi l nu form factor provides a
nontrivial test of our methods via comparison with CLEO data. We discuss the
use of HISQ valence quarks to calculate the K -> pi l nu form factor f_+^{K
pi}(0) and describe tests of our method.
