  We present a consistent calculation of the structure functions within a
light-front constituent quark model of the nucleon. Relativistic effects and
the relevance of the covariance constraints are analyzed for both polarized and
unpolarized parton distributions. Various models, which differ in their gluonic
structure at the hadronic scale, are investigated. The results of the full
covariant calculation are compared with those of a non-relativistic
approximation to show the structure and magnitude of the differences.
