Classical management theory is sometimes called "scientific management," an approach pioneered by Frederick Winslow Taylor (in fact, the approach is sometimes called "Taylorism". Taylor's focus was on industrial management. He was obsessed with fostering efficiency, and he suggested that managers do this in a number of different ways. First, he advocated specialization to the extreme. Workers should focus not just on a single job, but on a single task that was part of a rigid division of labor. He also suggested that workers should receive economic incentives to be more productive. From a management perspective, classical management was unitary. Management decisions, ranging from personnel to production, were made by one manager, whose dictates were implemented by a series of middle managers. Classical management theory is based on the assumption that people are driven by purely economic motives. This assumption, which can be traced back to the writings of eighteenth-century economists, does not take other factors into account. Human relations management theory is, on the other hand, based on these non-economic motives. It assumes that workers need to feel that their work has value (beyond the purely economic) and that the workplace should be a space where positive social interactions led to increased productivity. Rather than simply "scoring" workers and rewarding them for efficiency, an approach which tended to foster an atmosphere of relentless competition in the workplace, managers should encourage workers to adopt a cooperative approach, one which emphasized the importance of social interaction among workers. So, unlike classical, or "scientific" management, human relations management assumes that people were motivated by the need for social interactions.
As for comparisons between the two approaches, it should be noted that both are, in the final analysis, intended to make more money for business owners. Human relations management techniques, no less than classical ones, are ways to make workers more efficient and easier to control and, for lack of a better word, manage.