<p>There are works teaching fundamental skills, depending on the stage of the child's development and their "sensitive periods for learning." They start with sensorial and practical life skills. These, while providing the obvious experiences, also have indirect aims that introduce concepts for higher level learning - hand movements for writing, gauging pressure, fractions, etc. - and they keenly develop their senses for listening, feeling, and discriminating. Later in the progression, the children move into more academic learning in very hands-on ways. They learn their letters by shape and feel, they learn their numbers concretely, they learn relationships and concepts in concrete/hands-on ways. The primary years prepare a child for the focus, concentration, indendent thinking, and problem solving necessary for higher-level learning.</p>