In this article „constructive research of development” is pointed out as a central task of mathematics education, which stresses the constructive role of this domain for improvements in instructional practice. The steps of such research are described by examples out of our own project named TELEMA, which means: „Aids in mathematical instruction by special schoolbooks for pupils of lower mathematical ability”. The gap between theory and practice in mathematics education may be bridged in a better manner, if researchers pay more attention to methods of research as described here. © 1992, GDM - Gesellschaft für Didaktik der Mathematik. All rights reserved.