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The following process was used to identify standards and benchmarks for science:

Identification of Significant Reports
Three reports were identified as significant for representing current thinking on content standards in science: the National Science Education Standards (National Research Council, 1994), Project 2061's Benchmarks for Science Literacy (1993), and the National Science Teachers Association's (NSTA) Scope, Sequence, and Coordination of Secondary School Science: The Content Core (Pearsall, 1993). A total of seventeen additional documents were found useful for citation support of the benchmarks. These documents include California Department of Education's Science Framework for California Public Schools (1991) and three reports from the National Assessment of Educational Progress, Science Objectives for 1990, Exercise Specifications for 1994 NAEP, and Science Framework for the 1996 National Assessment of Educational Progress. The New Standards Project has published three documents that report science standards and benchmarks at elementary, middle, and high school levels. Those documents are Performance Standards: English Language Arts, Mathematics, Science, Applied Learning, Volume 1, Elementary School (1997a); Performance Standards: English Language Arts, Mathematics, Science, Applied Learning, Volume 2, Middle School (1997b); and Performance Standards: English Language Arts, Mathematics, Science, Applied Learning, Volume 3, High School (1997c). The International Baccalaureate Organization has published curriculum material that identifies significant content in science. Those documents are International Baccalaureate Biology (1996b); Chemistry (1996c); Environmental Systems (1996f); and Physics (1996i); Middle Years Programme: Sciences (1995f); and Primary Years Programme: Making it Happen in the Classroom (1996). The inclusion of the Primary Years is new with this edition.

The Third International Mathematics and Science Study (TIMSS), a large-scale, cross-national comparative study of math and science curricula, has made available to the public about two?thirds of the mathematics and science items administered to students in 1994?95. Of interest for this study were all items used for populations 1 and 2; for population 3, in keeping with the stated purpose of this study (see Process of this work), only literacy items were reviewed. The International Association for the Evaluation of Educational Achievement (IEA) published TIMSS Science Items: Released Set For Population 1 (Third and Fourth Grade) (1998d); TIMSS Science Items: Released Set For Population 2 (Seventh and Eighth grade) (1998e);and Released Item Set For the Final year of Secondary School: Mathematics and Science Literacy, Advanced Mathematics, and Physics (1998c).

Finally, McREL has published a study entitled A Distillation of Subject-Matter Content For the Subject-Areas of Language Arts, Mathematics, and Science (Kendall, Snyder, Schintgen, Wahlquist, & Marzano, 1999). Researchers at McREL reviewed a selected set of highly rated state standards within each subject area, examining them for common content. The McREL analysis resulted in the identification of the significant subject-area content that consistently appeared within these top rated documents.

Selection of the Reference Document
The National Research Council's National Science Education Standards was selected as the reference document. The effort was supported by the National Science Foundation, the U.S. Department of Education, and the National Aeronautics and Space Administration, among others. It represents the combined efforts of teachers, scientists, and science educators across the country.

Identification of Standards and Benchmarks
With this edition of Content Knowledge, the science standards and benchmarks have been revised. The number of standards has been reduced from 16 to 13, and the benchmarks reorganized beneath the revised set of standards. Although a number of standards have been altered in some way, the most significant changes were made in the life and physical sciences. The reorganization was undertaken to provide clearer differentiation between the standards, and thus better placement of the benchmarks. A number of benchmarks have been rewritten to accommodate changes at the standard level, or to combine very similar ideas. The original set of standards and benchmarks was developed from both the NRC standards document and 2061's Benchmarks. Each source document had a significantly different standards structure, which made a resolution problematic. The content standards from NRC, which "outline what students should know, understand, and be able to do in natural science" (p. 103), are grouped into categories at three grade levels (K-4, 5-8, and 9-12). The number of standards, however, varies by grade level within each of seven categories:

Science as inquiry
Physical science
Life science
Earth and space science
Science and technology
Science in personal and social perspectives
History and nature of science
A final area, "unifying concepts and processes," is not articulated for grade levels, but is intended for development across K-12 science education.

Science information in NRC's document is articulated for K-12 at the category level, but not at the standard level. That is, each standard and its associated content appears only once, and at one level (K-4, 5-8, or 9-12). For example, in the physical sciences under the heading "Earth and space science," a standard with the topic "Objects in the sky" appears with two related standards at grades K-4 only; at grades 5-8, three standards are under that category, and a closely related topic is "Earth in the solar system." At grades 9-12, four standards cover the area, and the one nearest in content to "Earth in the solar system" or "Objects in the sky" is the "Origin and evolution of the universe." Thus, the 66 standards are closely related within six categories, but are not articulated across the grade ranges by standard. Since our model calls for the articulation of standards across grade levels wherever possible, some reorganization of content was necessary. Although in part the benchmarks were constructed into standards from "the ground up," there was strong guidance provided by the structure of standards available from Project 2061's Benchmarks for Science Literacy.

At the benchmark level, Project 2061's Benchmarks proved very useful for distinguishing content at the grade ranges selected for this study: K-2, 3-5, 6-8, and 9-12. Material from the NRC reference document was added to or revised in four cases: 1) when minor modification of a benchmark statement allowed for additional citation support, 2) when the original statement carried more than one basic idea and was divided into components, 3) when stylistic changes helped the sense of the statement, and 4) when benchmark statements not in the science standards document were added because the information was found to appear consistently in the other major documents identified for science.

Additionally, there were a few instances of content duplication across standards. In each case that the subject material appeared to be redundant across standards, it was also clear that the same benchmarks within a standard served the purpose of preparing students for more complex, related ideas at later benchmark levels. For this reason, the duplicates were not deleted as would otherwise be done, but cross-referenced in the citation log. (For more detail, see How the Subject-Area Sections are Structured.)

It should be noted that content that appears in the science documents but is closely related to technology will be found incorporated into that section. Such topics as the interaction of technology with science and with society will now be found in the technology section.

Integration of Information from Other Documents
The documents used to integrate information were NSTA's Content Core and the California Science Framework. In addition, Content Core and Project 2061's Benchmarks provided a means for evaluating whether additional benchmarks should be added to the reference document. If information found at the appropriate level in either document could not be found in the NRC document, it was identified for possible inclusion as an additional benchmark. A compiled list of this information was then compared against information in the California Science Framework and the three documents from NAEP. If the information was found to be present in at least two documents (Content Core and/or Benchmarks, and one of the four documents just cited), the information was synthesized as a new benchmark. Evidence for this process can be found by an examination of the "citation log" associated with each benchmark: if the benchmark does not show a reference to the NRC document, then it was added to the document using the process just described. Additional documents were cited to provide users with links from the benchmarks to supporting materials. Such documents were the Performance Standards series from New Standards and the series of science curriculum materials from the International Baccalaureate Organization.

Any benchmark that addressed content closely related to a test item in the TIMSS science assessment has been identified by indicating the test level of the matching TIMSS assessment item. Similarly, any benchmark that addresses science content that was also identified as important in the McREL study of top standards documents has been so identified by an asterisk at the end of the citation log, which appears just above and to the right of the benchmark.