“In the early days of high school proms, the nighttime dance served a similar function to a debutante ball. Early proms were times of firsts: the first adult social event for teenagers; the first time taking the family car out after dark; the first real dress-up affair; and so forth. Proms also served as a heavily-documented occasion, similar to a milestone event such as first communion or a wedding, in which the participants were taking an important step into a new stage in their lives. In earlier days, the prom may have also served as an announcement of engagement for the “best couple” after the prom court had been crowned and recognized.
While high school yearbooks did not start covering proms and including prom pictures until the 1930s and 1940s, historians, including Meghan Bretz, believe proms may have existed at colleges as early as the late 1800s. The journal of a male student at Amherst College in 1894 recounts an invitation and trip to an early prom at neighboring Smith College for women. The word prom at that time may just have been a fancy description for an ordinary junior or senior class dance, but prom soon took on larger-than-life meaning for high school students.” http://en.wikipedia.org/wiki/Prom