According to Rudolf Steiner's teachings, a first significant transformation process takes place around the age of 7, when the child gets its second teeth. With the change of teeth, the human being has formed a second body. This body is the product of the human being's soul and spirit. Here you can read a short extract from Steiner's lecture series «The Roots of Education».
«The first significant change in a child’s life occurs around the seventh year when the second teeth appear. The outer physical process of the change of teeth is itself very interesting. First we have the baby teeth, then the others force their way through as the first are pushed out. A superficial look at this process will see no farther than the actual change of teeth. But when we look into it more deeply (through means I will describe later in these lectures) we discover that this transformation can be observed throughout the child’s body, though more delicately than the actual change of teeth. The change of teeth is the most physical and basic expression of a subtle process that in fact occurs throughout the body.
Initial body is forced out
What really happens? Anyone can see how the human organism develops. We cut our nails, our hair, and we find that our skin flakes off. This demonstrates how physical substance is cast off from the surface as it is constantly pushed out from within. This pushing from within — which we observe in the change of teeth — is present throughout the whole human body. More exacting knowledge shows us that indeed the child gradually forced out the body received through inheritance; it was cast out. The first teeth are forced out, and likewise the child’s whole initial body is forced out.
At the change of teeth, a child stands before us with a body that — in contrast to the body at birth — is entirely formed anew. The body from birth has been cast out as are the first teeth, and a new body is formed. What is the nature of this more intimate process? The child’s first body was inherited. It is the result of a collaboration between the father and mother, so to speak, and it is formed from the earthly physical conditions.
But, just what is this physical body? It is the model that the Earth provides to the person as a model for true development as a human being. The soul and spirit aspect of a human being descends from a realm of soul and spirit where it lived prior to conception and birth. Before we became earthly beings in a physical body, we were all beings of soul and spirit in a soul and spirit realm. What we are given by our parents through inherited physical substance unites in embryonic life with what descends from a higher realm as pure spirit and soul.
Spirit and soul take hold of the physical body, whose origin is in the stream of inheritance. This physical body becomes its model, and on this model an entirely new human organism is formed, while the inherited organism is forced out.
Thus, when we consider a child between birth and the change of teeth we can say that the physical body’s existence is due to physical inheritance alone. But, two other forces then combine to work on this physical body. First is the force of those elements the human being brought with it to Earth; the second is assimilated from the matter and substance of the Earth itself. By the time the teeth change, the human being has fashioned a second body modeled after the inherited body, and that second body is the product of the human soul and spirit.
Having arrived at such conclusions by observing the human being more intimately, one will naturally be aware of objections that may be raised; such objections are obvious. One is bound to ask: Can’t you see that a likeness to the parents often appears after the change of teeth — that, therefore, a person is still subject to the laws of inheritance, even after the change of teeth? One could raise a number of similar objections.
Let’s consider just this one: We have a model that comes from the stream of inheritance. On this model the spirit and soul develop the second human being. But when something is built from a model we don’t expect to find a complete dissimilarity to the model; thus, it should be clear that the human spirit and soul use the model’s existence to build up the second human organism in its likeness.
From the realm of spirit and soul
Nevertheless, when you can perceive and recognize what really occurs, you discover something. Certain children come into their second organism between nine and eleven, and this second body is almost identical to the initial, inherited organism. With other children, one may notice a dissimilarity between the second organism and the first, and it is clear that something very different is working its way from the center of their being. In truth, we see every variation between these two extremes. While the human spirit and soul aspect is developing the second organism, it tries most of all to conform to the being it brings with it from the realm of spirit and soul.
A conflict thus arises between what is intended to built as the second organism and what the first organism received through inheritance. Depending on whether thy have had a stronger or weaker spiritual and soul existence, human beings can either give their second organism an individual form that is strongly impregnated with soul forces, or, if they descend from the spiritual world with weaker forces, stay as closely as possible to the model.»
(Source: Rudolf Steiner: The Roots of Education, AP, 1996, 5 Lectures, Bern, 1924)