The Wolf-Villain model for growing surfaces is investigated using the
height-height correlation function and the structure factor. Both func
tions show an unusual scaling behaviour that can be attributed to the
time dependence of the average step size and is characterized by a new
exponent. A modified scaling law is introduced which may describe qui
te generally the crossover behaviour in models of this kind. It leads
to a very different classification of the model than has been inferred
from the exponents obtained by measuring the width of the surface as
a function of time and system size.