  The appearance of a light composite $0^+$ scalar resonance in nearly
conformal gauge-fermion theories motivates further study of the low energy
structure of these theories. To this end, we present a nonperturbative lattice
calculation of s-wave scattering of Goldstone bosons in the maximal-isospin
channel in SU(3) gauge theory with $N_f=8$ light, degenerate flavors. The
scattering phase shift is measured both for different values of the underlying
fermion mass and for different values of the scattering momentum. We examine
the effect of a light flavor-singlet scalar (reported in earlier studies) on
Goldstone boson scattering, employing a dilaton effective field theory (EFT) at
the tree level. The EFT gives a good description of the scattering data,
insofar as the magnitude of deviations between EFT and lattice data are no
larger than the expected size of next-to-leading order corrections in the EFT.
