Critical Thinking Across the Curriculum: What It Actually Is and How to Teach It

Critical thinking is the most commonly cited educational goal and the most frequently undefined one. Every school mission statement includes it. Relatively few specify what it means, how it develops, or how instruction would differ if it were taken seriously.

The vagueness is not trivial. "Develop critical thinking" is not an instructional goal — it's a category. The category contains specific, teachable skills that look different in different disciplines, develop through different kinds of practice, and are assessed through different kinds of tasks. Understanding what critical thinking actually is allows teachers to design instruction that develops it, rather than hoping it emerges from exposure to good content.

What Critical Thinking Is

Research on critical thinking — from Ennis, Facione, and more recently the APA Delphi Report — identifies critical thinking as skilled, purposeful, reflective judgment about what to believe or do. It includes:

• Interpretation: Understanding the meaning of information — what is being claimed, with what significance
• Analysis: Breaking claims and arguments into components — identifying conclusions, premises, assumptions, evidence
• Evaluation: Assessing the credibility of sources and the logical strength of arguments
• Inference: Drawing warranted conclusions from evidence
• Explanation: Articulating reasoning clearly — not just what you concluded but why
• Self-regulation: Examining one's own reasoning for biases, assumptions, and gaps

These are not abstract virtues. They're specific cognitive activities that can be practiced, improved, and assessed.

What Critical Thinking Is Not

A general intelligence: Critical thinking is not intelligence. High-intelligence students can reason poorly; careful reasoning can be developed in students across ability ranges.

Automatically transferred across domains: Critical thinking in mathematics (evaluating proofs) is related to but not identical to critical thinking in history (evaluating sources) or science (evaluating experimental design). The skills transfer partially, not automatically. Students need practice in disciplinary reasoning within each discipline.

Developed by simply asking "why?": Asking "why?" doesn't develop critical thinking — it depends on what students do with the question. "Why do you think that?" followed by a substantive examination of the reasoning does; "why do you think that?" as a rhetorical question the teacher immediately answers doesn't.

Domain-Specific Critical Thinking

Every discipline has its own epistemic standards — its own ways of knowing, its own criteria for good evidence, its own standards for valid reasoning. Teaching critical thinking in a discipline means teaching those standards explicitly.

In science: What counts as good evidence? Why do scientists require replication? What makes a methodology appropriate for a research question? What is the difference between a hypothesis and a theory? Students who understand how scientific knowledge is made are thinking critically about science.

In history: How do historians evaluate primary sources? What is the difference between a primary source that is reliable for one purpose and unreliable for another? How do competing historical interpretations handle the same evidence differently? Sourcing, contextualization, and corroboration are disciplinary critical thinking.

In mathematics: What makes a proof valid? What is an assumption, and how does changing assumptions change conclusions? When is a counterexample sufficient to disprove a claim? Mathematical reasoning is its own form of critical thinking.

In English and literature: What evidence in the text supports this interpretation? What alternative interpretations does the evidence support? How does the author's context shape the work's meaning? Textual reasoning is literary critical thinking.

How to Develop Critical Thinking in Practice

Make reasoning visible: The most valuable instructional move for critical thinking development is requiring students to explain their reasoning, not just their conclusions. "Why?" and "how do you know?" asked consistently — and received with genuine curiosity rather than as evaluative judgment — develop the habit of examined reasoning.

Practice argument analysis: Present students with arguments and ask them to identify the claim, the evidence, the assumptions, and the potential counterarguments. This decomposes the structure of reasoning and makes each component visible.

Assign reading that makes disagreement explicit: Texts that present competing arguments — historians who interpret the same events differently, scientists who draw different conclusions from the same data, literary critics who read the same text in incompatible ways — require students to evaluate arguments rather than simply receive information.

Resist providing conclusions: Teachers who summarize the lesson's conclusion rather than requiring students to construct it are doing the critical thinking for them. Productive struggle toward conclusions develops the reasoning that receiving them does not.

LessonDraft can help you design critical thinking activities, argument analysis tasks, and reasoning-focused discussions for any subject and grade level.

Critical thinking taught explicitly — through specific reasoning practices within specific disciplines — produces students who examine their own beliefs, evaluate evidence, and construct justified positions. This is the habit of mind that secondary education exists to develop. Taking it seriously means making reasoning visible, disciplinary, and consistently practiced.