The report includes ACT test results from all 50 states and the District of Columbia.

"The percentage of ACT-tested graduates who met or surpassed the ACT College Readiness Benchmark in math—suggesting they are ready to succeed in a first-year college algebra class—fell to its lowest level since 2004," the report declared, with only 40 percent of 2018 graduates meeting the benchmark, "down from a high of 46% in 2012."

The average score on the ACT math test dropped to its lowest level in 20 years — 20.5 on a scale of 1 to 36. American students scored 21.1 in 2012 and 20.7 last year.

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"The negative trend in math readiness is a red flag for our country, given the growing importance of math and science skills in the increasingly tech-driven US and global job market," said ACT CEO Marten Roorda. "It is vital that we turn this trend around for the next generation and make sure students are learning the math skills they need for success in college and career."

But it's not just math scores that have parents and educators concerned. Scores in other subjects are also falling.

"Readiness in English has also been trending down over the past several years, dropping from 64% in 2015 to 60% this year, the lowest level since the benchmarks were introduced," according to the report. "Readiness levels in reading (46%) and science (36%) were both down one percentage point from last year but are showing no long-term trends either upward or downward. Science remains the subject area in which students are least likely to be prepared for college coursework."