Mathematical tasks can be classified in a number of ways. While Galbraith & Haines (2001), for example, distinguish among mechanical, interpretative and constructive tasks, Smith et at. (1996) divide tasks into the following three categories: (A) factual knowledge, comprehension and routine use of procedures; (B) information transfer and application in new situations; and (C) identifying and interpreting; implications, conjectures and comparisons and evaluation. Having briefly summarized these and some other mathematical tasks classifications, this paper presents and critically examines the TIMSS 2003 mathematics cognitive domains. As a part of the TIMSS 2003 project these cognitive domains - knowing facts and roles, vising concepts, solving routine problems, and reasoning - were operationalized for the content domain of algebra in grade 8 and the paper gives a sample of the developed tasks that are fully available on the Internet (see www.matf.bg.ac.yu/čdjk/drafl2.pdfanA www.matf.bg.ac.yn/čdjk/yu20item.pdf). Through the examination and operationalization of the TIMSS assessment framework several implications for research and professional development of mathematics teachers have been realized. The article presents three of them dealing with an elaborated item classification, its empirical validation and a didactical preparation of teachers including operationalizations of the chosen task classification/taxonomy.