  Given $r \in \mathbf{N},$ let $\lambda$ be a partition of $r$ with at most
two parts. Let $\mathbf{F}$ be a field of characteristic 3. Write $M^\lambda$
for the $\mathbf{F}S_r$-permutation module corresponding to the action of the
symmetric group $S_r$ on the cosets of the maximal Young subgroup $S_\lambda.$
We construct a full set of central primitive idempotents in
$\text{End}_{\mathbf{F} S_r}(M^\lambda)$ in this case. We also determine the
Young module corresponding to each primitive idempotent that we construct.
