question represents the implemented curriculum, "How is instruction organized?", while the fourth, "What have students learned?", corresponds to the attained curriculum.
In order to make sense of the TIMSS data and analyses, it is important to know how the researchers conceptualized—and then investigated—several elements of educational systems. Analyses that explore connections among these elements are likely to be most productive in enabling valid interpretations and conclusions. For instance, information gathered on the content and use of textbooks provides a view of the curriculum that is complementary to data gathered on curriculum frameworks and tests. Knowing what is in textbooks and how widely they are used or whether and how they are even required offers insight into the potential influence of curriculum material on what students have opportunities to learn. Yet such information does not necessarily provide insight into the curriculum that students encounter in the classroom. Teachers' decisions about the organization and presentation of material also shape the curriculum. And knowing what students are taught still would not tell us what any particular student experiences, as mediated by his or her own interpretations. All these differences in meaning of curriculum highlight the interface between intended and implemented curriculum.
There are many different ways to interpret what is meant by curriculum. No one is somehow "right"; instead, the interpretation depends on the questions one is trying to answer about curriculum. In examining data, it is important to understand how curriculum is being defined. What did the TIMSS mean by, and how did researchers gather data on, documents and texts — the intended curriculum? On instructional practices—the implemented curriculum? On student learning—the attained curriculum? Understanding their meanings is crucial to interpreting the TIMSS findings.
The intended curriculum: TIMSS focused on three elements of the intended curriculum. First, researchers gathered and examined a variety of documents from each country that offered clues to the curriculum, as it was publicly defined.5 In many countries, the intended curriculum is articulated nationally, through framework documents. In some countries, such as the United States and Switzerland, the curriculum is for the most part specified at the state, district, or canton6—not the national—level. In all cases, the researchers read and analyzed curriculum guides and lists of objectives.
Textbooks comprised a second element of the curriculum examined by TIMSS researchers. Researchers assembled a collection of mathematics and science textbooks from each country. Approximately 1,600 teachers' guides and textbooks were analyzed across participating countries. Wherever possible, the materials were selected to represent those used by a majority of a given nation's students.