We have extended staggered chiral perturbation theory (SχPT) to O(a 2 p 2 ), O(a 4 ), and O(a 2 m), the orders necessary for a full next-to-leading order (NLO) calculation of pseudo-Goldstone boson (PGB) masses and decay constants including taste-symmetry violations. We present predictions relating SO(4) taste-breaking splittings in masses, pseudoscalar decay constants, and dispersion relations. These can be used to test the 4 √ Det trick.