The principle of the permanence of the rules of calculation is contrasted with the concretization permanence principle. Both apply to situations where some arithmetical operation known to children for numbers of a certain kind is to be extended to include further numbers. (MNS)

A classification of the simple combinatorial configurations which correspond to various cases of distribution and ordering of objects into boxes is given (in French). Concrete descriptions, structured relations, translations, and formalizations are discussed. (MNS)

The importance of teaching computational estimation is discussed, with note of its increased significance because of widespread use of calculators and the need to develop number sense. The reason for its failure to be taught is traced to the multiplicity of methods, and some detailed suggestions are therefore presented. (MNS)

A didactic principle of operative concept formation is described and explained. It is argued that this principle meets current demands for practical geometric activities with concrete forms and for the exploration of the primordial relation between geometry and reality. (MK)

Mathematical modeling is defined. Examples are used to show that there are models available which illustrate both the traditional use of mathematics in the physical science and its newer use in nonphysical disciplines, and which are at a suitable level for teaching in schools. (Author/MK)

Ratio and proportion are discussed by giving examples of a child's view of the concept. Instructional suggestions are given. (MK)