Evaluating Models & Explanations

Science doesn't progress by simply collecting facts—it advances by building models and explanations that account for observations, and then rigorously testing whether those models hold up against new data. Throughout history, the ability to evaluate competing explanations has been the driving force behind every major scientific breakthrough, from understanding planetary motion to decoding the structure of DNA.

These examples illustrate a core truth: scientists don't just propose ideas, they critically evaluate them against available data. On the ACT Science section, you'll be asked to do exactly this—determine whether new evidence supports, weakens, or is irrelevant to a given model or explanation. This lesson will teach you how to approach these questions systematically.

Before diving into ACT-specific strategies, you need to understand the foundational ideas that underlie every model-evaluation question. A scientific model is a simplified representation of a natural phenomenon—it can be a diagram, a set of equations, or even a verbal description that explains how or why something happens. An explanation is a specific claim about cause and effect within that model. Your job on the ACT is to judge whether evidence aligns with these models.

The diagram below shows the decision-making process you should follow when the ACT asks you to evaluate a model against new evidence. This flowchart captures the logical steps that scientists—and successful test-takers—use every time they assess whether data supports or contradicts an explanation.

Notice that the flowchart begins with reading the model carefully and identifying its key predictions—the specific claims the model makes about what should happen. This is the most critical step. If you skip it and jump straight to the data, you won't have a clear benchmark against which to compare the results. Always ask yourself: "What does this model say should happen?" Then look at what actually happened.

On the ACT Science section, model-evaluation questions appear most frequently in Conflicting Viewpoints passages and Research Summaries passages. In Conflicting Viewpoints, two or more scientists present different models or explanations for the same phenomenon, and you must determine which model is best supported by given evidence. In Research Summaries, you are often asked whether the results of an experiment are consistent with a particular hypothesis.

The Three-Step Method

To handle these questions efficiently under time pressure, use this streamlined approach. Step 1: Isolate the claim. What specifically does the model or scientist say? Reduce it to a single testable prediction—for example, "Scientist 1 says that increasing temperature will increase reaction rate." Step 2: Locate the relevant data. Find the table, graph, or passage text that addresses the same variable the claim mentions. Don't get distracted by data about other variables. Step 3: Compare and conclude. Does the data confirm or contradict the claim? If the data shows that increasing temperature did increase reaction rate, the model is supported. If the data shows no change or a decrease, the model is weakened.

Common Question Phrasings

• "Which of the following findings, if true, would most strengthen Scientist 2's hypothesis?"
• "The results of Experiment 3 are most consistent with which model?"
• "Which observation would most weaken the explanation given in the passage?"
• "Based on Scientist 1's model, which prediction about the new data would be expected?"
• "Do the data in Table 2 support or contradict Hypothesis A?"

Not all model-evaluation questions are the same. The ACT uses several distinct formats, each requiring a slightly different strategy. The diagram below classifies these into four categories, and the table that follows provides a deeper breakdown with example phrasings for each type.

Let's walk through a realistic ACT-style passage and question. Imagine a passage presenting two scientists debating why a local lake's fish population declined.

Question: Which piece of evidence most weakens Scientist 1's claim?

Students who do well on model-evaluation questions tend to share certain habits, while those who struggle often fall into predictable traps. The table below contrasts effective approaches with common mistakes, so you can recognize pitfalls before they cost you points.

The model-evaluation skills tested on the ACT are not just test-day tricks—they reflect the same reasoning framework used in college-level science, graduate research, and professional fields like medicine and engineering. Understanding how ACT-level evaluation connects to more advanced scientific reasoning will help you see the bigger picture and actually retain these skills.

As you move into college science courses, you'll encounter increasingly complex models with more variables and less clear-cut answers. The fundamental skill, however, remains the same: compare what a model predicts with what the data actually shows. Mastering this on the ACT gives you a genuine head start in scientific thinking, not just a higher score.

Test your understanding with these five problems, which increase in difficulty. For each, try the three-step method—isolate the claim, locate the data, compare and conclude—before checking the answer.