  To any Schur polynomial $s_{\lambda}$ one can associated its derived
polynomials $s_{\lambda}{(i)}$ $i=0,\ldots,|\lambda|$ by the rule
$$s_{\lambda}(x_1+t,\ldots,x_n+t) = \sum_i s_{\lambda}^{(i)}(x_1,\ldots,x_n)
t^i.$$ We conjecture that $$(s_{\lambda}^{(i)})^2 - s_{\lambda}^{(i-1)}
s_{\lambda}^{(i+1)}$$ is always Schur positive and prove this when $i=1$ for
rectangles $\lambda = (k^\ell)$, for hooks $\lambda = (k, 1^{\ell -1})$, and
when $\lambda = (k,k,1)$ or $\lambda = (3,2^{k-1})$.
