  We develop a formalism to evaluate the Sivers function. The approach is well
suited for calculations which use constituent quark models to describe the
structure of the nucleon. A non-relativistic reduction of the scheme is
performed and applied to the Isgur-Karl model of hadron structure. The results
obtained are consistent with a sizable Sivers effect and the signs for the u
and d flavor contributions turn out to be opposite. This pattern is in
agreement with the one found analyzing, in the same model, the impact parameter
dependent generalized parton distributions. The Burkardt Sum Rule turns out to
be fulfilled to a large extent. We estimate the QCD evolution of our results
from the momentum scale of the model to the experimental one and obtain
reasonable agreement with the available data.
