Why do students have summer vacation? One common answer is that it's a holdover from when America was more rural and needed children to help out on the farm, but even just a small amount of introspection suggests that answer is wrong. Even if you know very little about the practical side of farming, think for just a moment about what are probably the most time-sensitive and busiest periods for a farmer: spring planting and fall harvest. Not summer!
I'm not claiming to have made any great discovery here that summer vacation didn't start as result of following some typical pattern of agricultural production. Mess around on the web a bit, and you'll find more accurate historical descriptions of how summer vacation got started (for example, here's one from a 2008 issue of TIME magazine and here's one from the Washington Post last spring). My discussion here draws heavily on a 2002 book by Kenneth M. Gold, a professor of education at the City University of New York, called School's In: The History of Summer Vacation in American Public Schools.
Gold points out that back in the early 19th century, US schools followed two main patterns. Rural schools typically had two terms: a winter term and a summer one, with spring and fall available for children to help with planting and harvesting. The school terms in rural schools were relatively short: 2-3 months each. In contrast, in urban areas early in the first half of the 19th century, it was fairly common for school districts to have 240 days or more of school per year, often in the form of four quarters spread over the year, each separated by a week of official vacation. However, whatever the length of the school term, actual school attendance was often not compulsory.
In the second half of the 19th century, school reformers who wanted to standardize the school year found themselves wanting to length the rural school year and to shorten the urban school year, ultimately ending up by the early 20th century with the modern school year of about 180 days. Indeed, Gold cites an 1892 report by the U.S. Commissioner of Education William Torrey Harris which sharply criticized "the steady reduction that our schools have suffered" as urban schools had reduced their school days down toward 200 per year over the preceding decades.
With these changes, why did summer vacation arise as a standard pattern during the second half of the 19th century, when it had not been common in either rural or urban areas before that? At various points, Gold notes a number of contributing factors.
1) Summer sessions of schools in the first half of the 19th century were often viewed as inferior by educators at that time. It's not clear that the summer sessions were inferior: for example, attendance didn't seem to drop off much. But the summer sessions were more often taught by young women, rather than by male schoolteachers.
2) School reformers often argued that students needed substantial vacation for their health. Horace Mann wrote that overtaxing students would lead to "a most pernicious influence on character and habits ... not infrequently is health itself destroyed by overstimulating the mind." This concern over health seemed to have two parts. One was that schoolhouses were unhealthy in the summer: education reformers of the time reminded teachers to keep windows open, to sprinkle floors with water, and to build schools with an eye to good air ventilation. Mann wrote that "the small size, ill arrangement, and foul air, of our schoolhouses, present serious obstacles to the health and growth of the bodies and minds of our children." The other concern over health was that overstudy would lead to ill-health, both mental and physical. An article in the Pennsylvania School Journal expressed concern that children "were growing up puny, lank, pallid, emaciated, round-shouldered, thin-breasted all because they were kept at study too long. Indeed, there was an entire medical literature of the time that "mental strain early in life" led to lifelong "impairment of medical and physical vigour."
Of course, these arguments were mainly deployed in urban areas as reasons for shortening the school year. In rural areas where the goal was to lengthen the school year, an opposite argument was deployed, that the brain was like a muscle that would develop with additional use.
3) Potential uses of a summer vacation for teachers and for students began to be discussed. For students, there were arguments over whether the brain was a muscle that should be exercised or relaxed during the summer. But there was also a widespread sense at the time, almost a social mythology, that summer should be a time for intense interaction with nature and outdoor play. For teachers, there was a sense that they also needed summer: as one writer put it, "Teachers need a summer vacation more than bad boys need a whipping." There was a sense in both urban and rural areas that something like a 180-day school, with a summer vacation, would be the sort of job that would be attractive to talented individuals and well-paid enough to make teaching a full-time career. For teachers as well, there was a conflict as to whether they should spend summers working on lesson plans or relaxing, but the slow professionalization of teaching meant that more teachers were using the summer at least partially for work.
4) More broadly, Gold argues that the idea of a standard summer vacation as widely practiced by the start of the 20th century grew out of a tension in the ways that people thought about annual patterns itself in the late 19th century. On one side, time was viewed as an annual cycle, not just for agricultural purposes, but as a series of community practices and celebrations linked to the seasons. On the other side, time was starting to be industrial, in a way that seasons mattered much less and the smooth coordination of production effort mattered more. A standard school year with a summer vacation both coordinated society along the lines of time, while offering a respect for seasonality as well.