Sally Reed was represented at the Supreme Court by Idaho lawyer Allen Derr, who argued that the Fourteenth Amendment forbids discrimination based on sex.

[2] After a series of appeals by both Sally and Cecil Reed, the Supreme Court considered the case and delivered a unanimous decision that held the Idaho Code's preference in favor of males was arbitrary and unconstitutional.

[1] In doing so, the Supreme Court ruled for the first time that the Equal Protection Clause of the Fourteenth Amendment prohibited differential treatment based on sex.

"[1] Chief Justice Burger's opinion said:[1] To give a mandatory preference to members of either sex over members of the other, merely to accomplish the elimination of hearings on the merits, is to make the very kind of arbitrary legislative choice forbidden by the Equal Protection Clause of the Fourteenth Amendment; and whatever may be said as to the positive values of avoiding intrafamily controversy, the choice in this context may not lawfully be mandated solely on the basis of sex.Before the Supreme Court decided the case, Idaho amended its statutes to eliminate the mandatory preference for males, effective July 1, 1972.

[3] Those who brought the case had hoped for a broader decision that would have deemed all classifications based on sex "suspect", a category the Supreme Court reserved for race.