The four punctuation rules the digital SAT actually tests
A large share of the Standard English Conventions questions on the digital SAT are what College Board calls boundaries: four choices that differ only in the punctuation at one spot in a sentence. Students treat them as a grammar test and try to remember rules. There is really one rule, and everything else is a special case of it.
The one check
Find the spot where the choices differ. Cover the choices. Ask two questions:
Is what comes before it a complete sentence? Is what comes after it a complete sentence?
A complete sentence has a subject and a main verb and could stand alone with a period. That is the entire test. The four marks the SAT cares about are each defined by the answer to those two questions.
1. The semicolon is a period
A semicolon joins two complete sentences. Both sides must be able to stand alone. If either side cannot, the semicolon is wrong. And if both sides can, a comma on its own is wrong, which is the trap in the next section.
This also covers the most common trick in the category: a sentence with however, therefore or for example in the middle. Those words do not join sentences. The results were promising; however, the sample was small needs the semicolon, because there is a complete sentence on each side and however is just a word sitting in the second one. A comma before however there is a comma splice, and it is offered as a choice every time.
2. The colon needs a complete sentence before it
What comes before a colon must stand alone. What comes after it can be anything: a list, a single word, an explanation, another full sentence. The SAT tests the first half of that far more than the second: a colon after such as or including or a verb is wrong because the left side is not finished.
3. Dashes come in pairs, or act like colons
A pair of dashes sets off an interruption, and both ends have to match. If the interruption opens with a dash it must close with a dash, not a comma. This is the second most common trap in the category: a choice that opens with a dash and closes with a comma, or the reverse.
A single dash behaves like a colon: complete sentence before it, anything after.
4. Commas do three jobs, and one thing they never do
A comma cannot join two complete sentences on its own. This is the comma splice, and it is the wrong answer on more boundaries questions than any other single mistake. If both sides pass the check, a comma alone is out.
A comma plus a joining word can. The results were promising, but the sample was small. The seven words that do this are for, and, nor, but, or, yet, so. Without one of them the comma needs to become a semicolon.
Commas around an interruption come in pairs, exactly like dashes. The sample, which was collected in 2019, was small needs both commas. One comma is never right for an interruption in the middle of a sentence.
No comma between a subject and its verb, however long the subject is. The sample collected by the team in 2019, was small is wrong, and the SAT offers it because a long subject makes the comma feel natural.
The method, in the time you have
Cover the choices. Find the boundary. Ask the two questions. Then, and only then, look at the four options and pick the mark whose rule matches what you found. On a typical question this takes twenty seconds, and the choices you did not look at could not tempt you.
Students who read the choices first spend the same twenty seconds and then another thirty deciding between two that both sound fine. Nearly every boundaries question has two choices that sound fine. The check is how you tell them apart without sounding them out.
Where the points are
In the timing logs I keep, boundaries questions are rarely a student’s wrong answers. They are the right but slow answers, correct in fifty seconds instead of twenty, and there are enough of them per module that the lost time lands on the harder questions at the end. Learning the check does not usually move accuracy much. It moves the clock, and the clock is where the score is.
College Board’s Question Bank filters by Boundaries. Do thirty with the choices covered, timing each one, and watch the number drop.