Adult-Targeted Market.

For the first half of the twentieth century the big designers targeted adult women since they or their husbands had the money to spend. Girls dressed in basic school clothes: plain dresses or cotton blouses, cardigan sweaters, and wool skirts in conformity with school dress codes. School fashions were created by anonymous designers at clothing manufacturers. While hemline height, colors, and so forth were influenced by Paris, the fashion capital's designers seldom made direct contributions to the wardrobe of girls. For dress-up occasions, girls wore versions of their mothers' clothing.

More Money.

But in the late 1950s and early 1960s teenagers had more money than previous generations. The postwar years had been prosperous, and girls often had incomes from part-time jobs or sizable allowances from their parents.

More Girls.

Also, there were more girls in that generation as...