For each test section, the number of correct answers are counted. (Points are not subtracted for incorrect answers; getting a question wrong has the same effect as skipping it entirely). The questions on the ACT change over time, so a scaling factor is used to ensure that a scaled 23 on a test taken in 2010 means the same as a scaled 23 on a test taken in 1998.
Each of the subject test scores (and the composite score, which is the average) range from 1 to 36, where higher numbers are better. The same rules apply to the subscores associated with subsections on each test (for example, the Rhetorical Skills subsection of the English test), except the scores for subsections range from 1 to 18. Notice that your subscores do not add up to your test score.
In addition to the four previously mentioned multiple choice tests, ACT offers a writing test that does not count towards the Composite Score. Essays for the writing exam are scored by two trained readers who rate it from 1 (little or no skill is demonstrated) to 6 (task is completed effectively); the scores are added to compute the Writing subscore. However, if the reviewers disagree by more than one point, a third reader will evaluate the essay as well.