  If general relativity (GR) describes the expansion of the Universe, the
observed cosmic acceleration implies the existence of a `dark energy'. However,
while the Universe is on average homogeneous on large scales, it is
inhomogeneous on smaller scales. While GR governs the dynamics of the
\emph{in}homogeneous Universe, the averaged \emph{homogeneous} Universe obeys
modified Einstein equations. Can such modifications alone explain the
acceleration? For a simple generic model with realistic initial conditions, we
show the answer to be `no'. Averaging effects negligibly influence the
cosmological dynamics.
