Germany's tradition of formal education dates back to the 1800's, when the three-tiered school system originated. Historically, the highest levels of education were reserved for a small percentage of the population, while the majority received a basic education followed by training in particular trades or vocations. As the economic strength of the country has grown, the number and variety of jobs requiring higher levels of education have increased, and a growing percentage of the school-age population has pursued study at the Realschule and the Gymnasium in order to achieve higher levels of certification. While the lowest level secondary school form (the Hauptschule) has become less popular, it continues to educate nearly 30 percent of German students, leading them to vocational training programs in their adolescent years and into the work force as they approach their late teens. The responsibility for primary and secondary education in Germany rests with state and local authorities. School funding derives primarily from the state level, and a redistribution of tax revenues among states gives them comparable budgets for funding their education systems. In addition, state funding formulas guarantee that schools within each state receive approximately equal funding. The Conference of Ministers of Education (KMK) coordinates education efforts on a national level through representation from each of the state ministries. The KMK has developed a set of voluntary standards and guidelines for school forms, a common curriculum, and mutual recognition of school completion qualifications, all of which are implemented by the individual states. As a result, each school form has clearly stated goals and expectations for students, and the teachers' instructional activities, lesson plans, and interactions with students reflect and support these goals and expectations. Although variations are found between states with centralized versus decentralized education systems, the KMK resolutions ensure a high degree of comparability in the academic process and in implementation of standards throughout Germany. The KMK standards for all Abitur examinations are perhaps the most obvious example of these state-adopted national standards. Another mechanism by which education has been standardized in Germany is through the regulation of textbooks. The state ministries of education publish lists of approved textbooks accompanied by regulations for their approval, introduction, and use. Schools within each state must choose their textbooks from these lists. At the Grundschulen we visited, grade level teachers indicated that they reviewed and selected textbooks together. In addition, many Grundschule and lower secondary-level teachers said that they base their course curriculum on the textbooks, since they know they conform to the state's curriculum guidelines.