In 1956, Benjamin Bloom, Max Englehart, Edward Furst, Walter Hill, and David Krathwohl created what is perhaps the single-most utilized model at all levels of education. This model was included in the publication titled: Taxonomy of Educational Objectives and eventually would come to be known simply as Bloom's taxonomy. The original taxonomy consisted of the following six levels: Knowledge, Comprehension, Application, Analysis, Synthesis, and Evaluation. Bloom's taxonomy provides a framework for categorizing the cognitive domains associated with learning such that educators can utilize them in constructing objectives for their curriculum.

Below is a an excerpt from the original publication's appendix in which the authors briefly summarize each of the six main categories. The levels above Knowledge were defined as "skills and abilities" and the assertion was made that one must first acquire knowledge of specific content before one is able to execute these skills and abilities. This created a linear hierarchical relationship between the levels which many have criticized.

• Knowledge “involves the recall of specifics and universals, the recall of methods and processes, or the recall of a pattern, structure, or setting.”
• Comprehension “refers to a type of understanding or apprehension such that the individual knows what is being communicated and can make use of the material or idea being communicated without necessarily relating it to other material or seeing its fullest implications.”
• Application refers to the “use of abstractions in particular and concrete situations.”
• Analysis represents the “breakdown of a communication into its constituent elements or parts such that the relative hierarchy of ideas is made clear and/or the relations between ideas expressed are made explicit.”
• Synthesis involves the “putting together of elements and parts so as to form a whole.”
• Evaluation engenders “judgments about the value of material and methods for given purposes.”
  • Taxonomy of Educational Objectives (Handbook One, pp. 201-207)

In 2001, a team of educators, cognitive psychologists, instructional researchers, and assessment specialists published an updated version of the model (pictured above) titled: A Taxonomy for Teaching, Learning, and Assessment. There are two visibly notable differences in the revised model. First, each level is described with a verb instead of a noun. This reflects a fundamental shift in the perception of the learning process as passive to a more active, student-centered process. Second, the top two levels have been switched so that Creating (Synthesis) is the highest level of cognitive functioning. Further, the authors included an additional taxonomy consisting of four knowledge domains. The domains of knowledge identified were: Factual, Conceptual, Procedural, and Meta-cognitive. Combining the cognitive domains of the original taxonomy with these new knowledge domains creates a useful tool for classifying objectives. The overall intent of the revision was to provide a framework which is more dynamic in its ability to aid in classifying objectives. The benefits of this revised classification process are discussed below.

• The bottom three levels of the taxonomy are often referred to as lower order thinking skills and the top three levels are often referred to as higher order thinking skills. As mentioned above, critics of Bloom's point to the linear progression of knowledge it suggests as being too general and overly-simplified. The hierarchy, taken at face value, implies that a student must start at the bottom and work their way to the top. Knowledge must come first, Understanding must come next, and so on. The criticism of this concept is not without merit. Of course there is a natural scaffolding necessary in the learning process which requires a foundation of facts and knowledge. However, to suggest that all things in all contexts must necessarily be taught and learned following this process is to ignore the dynamic nature of learning and the complexity of the human brain. It is our job as educators to utilize such a framework to meet our needs and the needs of our students while understanding its limitations and constraints.
• One way educators can utilize this framework without adhering to the linear implication is by classifying each of their objectives on a chart such as the one below. The chart includes the cognitive domains from the original taxonomy and the knowledge domains from the revised taxonomy. Depending on the level of the student and the course content, objectives may be skewed one way or another. However, it is desirable to have objectives spread as wide across the chart as possible. This indicates a course that is activating all levels of cognitive processing in a variety of contexts.

• The creation and classification of objectives is an essential component in the course alignment process. Simply put, course alignment means that one's instruction and assessment is explicitly linked to the learning objectives for the course. This relationship can (and should) be easily communicated to students. In communicating this alignment, students are more easily able to see the rationale behind assessments, the necessity of instruction, and the relevance of completing tasks and assignments.
• The process of classifying learning objectives necessitates cognitive processes for instructors which cause them to consider precisely what outcomes they desire and what evidence a student must produce to show mastery. With this evidence in mind, instructors can better select (or create) the most appropriate assessments and instructional activities. The process of creating objectives first, selecting assessments second, and determining instructional strategies last, is known as backwards design.
• One variation of backward design is the Understanding by Design (UbD) model created by Wiggins and McTighe (1998). Below is a white paper describing the UbD model in detail and a concept map which summarizes the UbD model.