  I discuss the size distribution ${\cal N}(S)$ of avalanches occurring at the
yielding transition of mean field (i.e., Hebraud-Lequeux) models of amorphous
solids. The size distribution follows a power law dependence of the form:
${\cal N}(S)\sim S^{-\tau}$. However (contrary to what is found in its
depinning counterpart) the value of $\tau$ depends on details of the dynamic
protocol used. For random triggering of avalanches I recover the $\tau=3/2$
exponent typical of mean field models, which in particular is valid for the
depinning case. However, for the physically relevant case of external loading
through a quasistatic increase of applied strain, a smaller exponent (close to
1) is obtained. This result is rationalized by mapping the problem to an
effective random walk in the presence of a moving absorbing boundary.
