  We compute the isospin $I= 0$ and 2 amplitudes for the decay of a kaon into
two pions by estimating the relevant hadronic matrix elements in the chiral
quark model. The results are parametrized in terms of the quark and gluon
condensates and of the constituent quark mass $M$. The latter is a parameter
characteristic of the model, that we restrict by matching the results in the
two $\gamma_5$-schemes (HV and NDR) of dimensional regularization. We find
that, for values of these parameters within the current determinations, the
$\Delta I= 1/2$ selection rule is well reproduced by means of the cumulative
effects of short-distance NLO Wilson coefficients, penguin diagrams,
non-factorizable soft-gluon corrections and meson-loop renormalization.
