Treated with dislike, distaste, much the same as a "second class citizen." Less important. Ostracized, at times.
(If the stepchild had red hair, and the parent didn't,
people would assume that the parent was the step-parent. This is obviously an ignorant assumption, since the
gene for red hair is not a "dominate"
gene, but a "recessive" gene -- it would skip generations before showing up again.)
In the state of
Alabama, it is well known that Auburn University will always be the Redheaded Stepchild to the University of
Alabama, when pertaining to
football and all other things athletic - and chess. RTR!