  In 2009, Maksa and P\'ales established an extension of the decomposition
theorem of Ng in the context of higher-order convexity notions. They proved
that a real function is Wright convex of order $n$ if and only if it can be
decomposed as the sum of a convex function of order $n$ and a polynomial
function of order at most $n$. Their proof was based on transfinite tools in
the background. The main purpose of this paper is to adopt the methods of a
paper of P\'ales published in 2020 and establish a new and elementary proof for
the theorem of Maksa and P\'ales.
