The top layer is the intended (or official) curriculum. After extensive deliberation and committee meetings, state and district officials publish curricular frameworks and courses of study in academic subjects from kindergarten through high school.

Consider science curriculum in California. The first science framework in 1990 laid out content standards, grade by grade, as to what teachers should teach and what students should learn. Since then, there have been revisions in the state framework (scienceframework-1).

The purposes of the science framework are stated clearly:

Educators have the opportunity to foster and inspire in students an interest in science; the goal is to have students gain the knowledge and skills necessary for California’s workforce to be competitive in the global, information-based economy of the twenty-first century….

This framework is intended to (1) organize the body of knowledge that students need to learn during their elementary and secondary school years; and (2) illuminate the methods of science that will be used to extend that knowledge during the students’ lifetimes.

Note that these purposes for the framework seek to have students leave school inspired and interested in science, equipped with knowledge and skills to enter the workforce, and conversant with how scientists think and act. Multiple and competing purposes drive this framework, a situation that has characterized science education for decades.

The California science standards are connected to approved textbooks that teachers use in their elementary and secondary school lessons and, further, the science standards are linked to the California Standards Test given at grades 5 and 8 and 10 and in the separate sciences (biology, earth science, chemistry, and physics) in grades 9-12. Thus, curriculum standards as a structure are connectedto the age-graded school, instructional materials for teaching the subject matter, and assessment of whether the content has been taught and whether students have learned what was taught. This, then, is the intended curriculum.

I say “intended” because once states adopt curricular frameworks in science they will have only a passing similarity to the science content and skills that teachers will teach once they close their classroom doors. In the real world of age-graded schools, pedagogy, assessment, and professional development are thoroughly entangled while the official curriculum too often sails above the clouds loosely tethered to what happens in classrooms. How can that be? The answer is in the other layers of the curriculum structure.

Teachers, working alone in their rooms, make up the second layer. They decide what to teach and how to present it. Their choices derive from their knowledge of the subject they teach (elementary and secondary school teachers differ greatly in their knowledge of science), their knowledge of children and youth, their beliefs about how teachers should teach and children should learn, prior experiences as a student, their affection or dislike for topics in the framework and textbook, and their attitudes toward the students they face daily. In fact, researchers continually find that teachers in the same building will teach different versions of the same course while claiming that they are teaching to the state standards and to the prevailing desired pedagogy. Thus, the intended curriculum and what teachers teach may overlap in the title of the course, key topics, and the same textbook, but can differ substantially in actual subject matter and daily lessons.

The taught curriculum overlaps with but differs significantly from what students take away from class. This is the third layer. Students pick up information and concepts from lessons. They also learn to answer teacher questions, review material, locate sources, seek help, avoid teachers’ intrusiveness, and act attentive. Moreover, children pick up ideas from class-mates, copy their teachers’ habits and tics, imitate their humor or sarcasm, or strive to be as autocratic or democratic as the adults. So, the learned curriculum differs from the intended and taught curricula.

And what students learn does not exactly mirror what is in the tested curriculum. Here, then, is the fourth layer of curriculum. Classroom, school, district, state, and national tests, often using multiple-choice and other short-answer items, capture some–but hardly all–of the official and taught curricula. To the degree that teachers and students attend to such tests, portions of the intended and taught curricula merge. Furthermore,  many of these tests seek to sort high achieving students from their lower-achieving peers. The information, ideas, and skills contained in test items for such purposes represent an even narrower band of knowledge.

There are, then, four curricular layers, not one unvarnished curriculum. The official curriculum, often derived from state curricular frameworks, professional associations, or national standards, is the top layer of the formal structure of content and skills that teachers are expected to teach and students learn. It is the exterior layer that reformers continually change in their effort to alter what teachers teach and students learn. But the official curriculum rests atop three other layers that assemble and distribute knowledge and skills in the age-graded school through pedagogy, assessment, and professional development: the taught, learned, and tested curricula.

I have omitted one important fact about this multi-layered curriculum. Previous reforms create the historical context for the multi-layered curriculum and influence the direction of contemporary reforms. This historical context is like a coral, a mass of skeletons from millions of animals built up that, over time, accumulates into reefs above and below the sea line. Its presence cannot be ignored neither by ships nor by inhabitants. Yet many eager reformers in science education do ignore the coral reefs, pay little attention to the historical context for the new science teaching and learning that they champion.

Having a four-layered structure called curriculum that has been changed time and again is precisely how reform-driven policymakers end up again and again confusing change with reform. In changing the exterior layer of the multi-layered curriculum, decision-makers are confident that they have now improved, nay, reformed the curriculum. They believe that teachers will teach more and better science, students will learn, and test scores will mirror those improvements. When the anticipated results fail to materialize in classroom lessons and student outcomes, confusion, disappointment, and disillusion occur.

Much of that confusion and ultimate disappointment over new science curricula over the past century, then, has had to deal with the discrepancies within and between the multi-layered curriculum and the historical coral reefs upon which it rests.