High school students’ scores on the ACT college admissions test have dropped to their lowest in more than three decades, showing a lack of student preparedness for college-level coursework, according to the nonprofit organization that administers the test.

Scores have been falling for six consecutive years, but the trend accelerated during the COVID-19 pandemic. Students in the class of 2023 whose scores were reported Wednesday were in their first year of high school when the virus reached the U.S.

“The hard truth is that we are not doing enough to ensure that graduates are truly ready for postsecondary success in college and career,” said Janet Godwin, chief executive officer for the nonprofit ACT.

The average ACT composite score for U.S. students was 19.5 out of 36. Last year, the average score was 19.8.

The average scores in reading, science and math all were below benchmarks the ACT says students must reach to have a high probability of success in first-year college courses. The average score in English was just above the benchmark but still declined compared to last year.

Many universities have made standardized admissions tests optional amid criticism that they favor the wealthy and put low-income students at a disadvantage. Some including the University of California system do not consider ACT or SAT scores even if submitted.

Ms. Godwin said the scores are still helpful for placing students in the right college courses and preparing academic advisors to better support students.

“In terms of college readiness, even in a test-optional environment, these kinds of objective test scores about academic readiness are incredibly important,” Ms. Godwin said.

At Denise Cabrera’s high school in Hawaii, all students are required to take the ACT as juniors. She said she would have taken it anyway to improve her chances of getting into college.

“Honestly, I’m unsure why the test was ever required because colleges can look at different qualities of the students who are applying outside of just a one-time test score,” said Denise, a 17-year-old senior at Waianae High School.

She is looking at schools including the California Institute of Technology, which implemented a five-year moratorium on the standardized test score requirements during the pandemic. Denise said she knows the school is not considering scores, but she does not want to limit her options elsewhere.

About 1.4 million students in the U.S. took the ACT this year, an increase from last year. However, the numbers have not returned to pre-pandemic levels. Ms. Godwin said she does not believe those numbers will ever fully recover, partly because of test-optional admission policies.

Of students who were tested, only 21 percent met benchmarks for success in college-level classes in all subjects. Research from the nonprofit shows students who meet those benchmarks have a 50 percent chance of earning a B or better and nearly a 75 percent chance of earning a C or better in corresponding courses.