9.1 Compositional Analysis Overview & Topic Sentences

The Compositional Analysis section is the smallest of the four STEP sections, but it is also the section most directly built on skills you have already developed in the Reading Comprehension and Grammar chapters. Instead of asking you to write an essay, every question presents a multiple-choice task that tests whether you can recognize good writing when you see it: the right topic sentence for a set of details, the right word to connect two ideas, the right order for a set of ideas, or the sentence that does not belong. This section rewards careful reading and logical judgment, not spelling or free composition.

What Compositional Analysis Tests

Across its 10 scored questions, Compositional Analysis asks you to evaluate short pieces of writing rather than produce your own. Typical tasks include:

• Choosing the best topic sentence for a set of supporting details
• Choosing the best transition or connector word between two ideas
• Choosing the most logical order for a scrambled set of sentences
• Choosing the most concise way to express an idea
• Identifying the one sentence that breaks a paragraph's cohesion
• Identifying capitalization or punctuation errors

Every one of these tasks has a single defensible correct answer once you apply the right rule, which is why Compositional Analysis, despite its "writing" label, behaves more like a logic-and-grammar hybrid than a creative-writing test.

Why This Section Deserves Real Study Time

Ten percent of the score can look easy to write off, especially next to Reading Comprehension's 40% and Grammar's 30%. That reasoning is a mistake for two reasons. First, ten points is still enough to move a borderline score across an institution's cutoff (some programs require 50, others 75), so every section matters proportionally. Second, and more importantly, this section costs you almost no new study time because it draws directly on skills you are already building elsewhere:

In other words, Compositional Analysis is partly a review section. Strong Reading and Grammar preparation should make most of these ten questions feel familiar rather than foreign.

Choosing the Best Topic Sentence

A topic sentence states a paragraph's main idea in general terms, while the sentences around it supply specific evidence, examples, or explanation. In the Reading Comprehension chapter, you practiced finding a topic sentence that was already written into a passage. Compositional Analysis flips that task: instead of finding the general statement, you must select or build it from a menu of options, using the supporting sentences as your evidence.

A correct topic sentence must satisfy two conditions at the same time:

1. Broad enough to cover every supporting sentence in the set, not just one or two of them.
2. Narrow enough that it does not introduce ideas or claims the supporting sentences do not actually support.

Most wrong answers fail one of these two tests. An option that repeats a single supporting detail is too narrow; an option that makes a sweeping claim well beyond what the details show is too broad.

Worked Example

Supporting sentences:

• Solar panels convert sunlight directly into electricity without releasing emissions during operation.
• Wind turbines use moving air to spin blades connected to generators, producing power with no fuel combustion.
• Hydropower plants generate electricity by channeling the force of flowing or falling water through turbines.
• Geothermal plants tap heat stored beneath the earth's surface to produce steam that drives turbines.

Candidate topic sentences: A. Renewable energy sources generate electricity through a variety of natural processes without burning fossil fuels. B. Solar panels are the most efficient form of renewable energy available today. C. Electricity has changed how people live over the last century. D. Wind turbines are becoming more common in coastal areas around the world.

Walking through each option: (B) singles out solar panels and makes an efficiency claim none of the four sentences addresses, so it is too narrow and unsupported. (C) is true in a general sense but has nothing to do with the specific mechanisms described, so it is far too broad. (D) describes only wind turbines and adds a claim about geography that the supporting sentences never mention, so it is too narrow. Only (A) is general enough to introduce all four energy sources while staying tied to what the supporting sentences actually describe — generating electricity without fossil fuels. (A) is the correct topic sentence.

Quick Strategy for Test Day

1. Read every supporting sentence first, before looking at the candidate topic sentences.
2. Cross off any candidate that only restates one supporting detail — it is too narrow.
3. Cross off any candidate that introduces information the supporting sentences never mention — it is too broad.
4. Whatever survives both cuts is your answer, even if a wrong option sounds more polished.