  Lattice QCD calculations with different staggered valence and sea quarks can
be used to improve determinations of quark masses, Gasser-Leutwyler couplings,
and other parameters relevant to phenomenology. We calculate the masses and
decay constants of flavored pions and kaons through next-to-leading order in
staggered-valence, staggered-sea mixed-action chiral perturbation theory. We
present the results in the valence-valence and valence-sea sectors, for all
tastes. As in unmixed theories, the taste-pseudoscalar, valence-valence mesons
are exact Goldstone bosons in the chiral limit, at non-zero lattice spacing.
The results reduce correctly when the valence and sea quark actions are
identical, connect smoothly to the continuum limit, and provide a way to
control light quark and gluon discretization errors in lattice calculations
performed with different staggered actions for the valence and sea quarks.
