The distribution function
PL(s) of the local order parameter
s in finite blocks of size
Ld is studied for Ising models for dimensionalities
d=2,3,and4 by Monte Carlo methods. A real-space renormalization group based on phenomenological scaling yields fairly accurate results for rather small
L (e.g., the standard exponents $\ensuremath{\beta}$ and $\ensuremath{\nu}$ for
d=3 are found as $\frac{2\ensuremath{\beta}}{\ensuremath{\nu}}=1.03\ifmmode\pm\else\textpm\fi{}0.01$, $\frac{1}{\ensuremath{\nu}}=1.60\ifmmode\pm\else\textpm\fi{}0.05$). The method can easily be generalized to arbitrary Hamiltonians, including spin dimensionalities
n>1.