  The Weinberg theorem for the pion-pion scattering is proved analytically in
full detail for quark models in the ladder truncation. The proof is displayed
with Feynman diagrams. The axial and vector Ward identities, for the quark
propagator and for the ladder, exactly cancel any model dependence. Off mass
shell and finite size effects are included in the quark-antiquark pion Bethe
Salpeter vertices. This is applied to compute the isospin 0, 1 and 2 scattering
matrices off the mass shell .
