  We generalise Bray's self-consistent screening approximation to describe the
critical dynamics of the $\phi^4$ theory. In order to obtain the dynamical
exponent $z$, we have to make an ansatz for the form of the scaling functions,
which fortunately can be much constrained by general arguments. Numerical
values of $z$ for $d=3$, and $n=1,...,10$ are obtained using two different
ans\"atze, and differ by a very small amount. In particular, the value of $z
\simeq 2.115$ obtained for the 3-d Ising model agrees well with recent
Monte-Carlo simulations.
