Bill Gates, a key godfather of the Common Core subject-matter standards, wrote five years ago that the national standards “will improve education for millions of students,” but a groundbreaking new study shows that Common Core has actually decreased the level of student achievement.

With irresistible prodding by Gates and then-President Obama, the Common Core national standards were adopted by the vast majority of states, which have also adopted tests and curricula aligned with those standards.

But a new large-scale study by the federally funded Center for Standards, Alignment, Instruction, and Learning (C-SAIL) has found that since the adoption of Common Core there has been a decline in key test scores.

C-SAIL researchers analyzed changes in student performance on the National Assessment of Educational Progress, or NAEP, from 2010 to 2017.

They had assumed that Common Core would raise student performance on the NAEP exam, but they were in for a surprise.

“Contrary to our expectation,” they reported, the data revealed that the Common Core standards produced “significant negative effects on 4th graders’ reading achievement during the 7 years after the adoption of the new standards.”

When analyzing the results of a selected group of states, fourth-grade reading achievement would have improved more “had the states continued with their old standards, thus reflecting negative effects of the new [Common Core] standards.”

In other words, if those states had ignored the entreaties by Gates, Obama, et al., they would have been better off.

In addition to the decline in reading performance among fourth graders, the C-SAIL study also found that Common Core “had a significant negative effect on 8th graders’ math achievement.”

What’s more, the performance of students declined significantly in specific reading and math categories, such as literacy experience and numbers properties, the longer Common Core was in effect.

Study co-author Mengli Song said: “It’s rather unexpected. The magnitude of the negative effects [of Common Core] tend to increase over time. That’s a little troubling.”

Actually, it’s extremely troubling.

Some blame the failure of Common Core on process issues, such as lack of adequate teacher training, but the key culprits are the standards themselves and the type of teaching promoted by Common Core.

When Common Core was first being adopted by states, James Milgram, a Stanford math professor who served on a key Common Core committee, warned that by the end of the fifth grade the material covered by Common Core’s math standards “was more than a year behind the early grade expectations of high-achieving countries,” and that “by the end of the seventh grade, [Common] Core standards are roughly two years behind.”

By high school, “Common Core — in its fullness — does not prepare students even for a full pre-calculus class,” notes Ze’ev Wurman, a former senior education policy advisor under President George W. Bush.

According to the Boston-based Pioneer Institute, which has closely studied Common Core, “Instead of accelerating the curriculum to more advanced topics and following the practices of leading international competitors, Common Core’s politically-driven process resulted in the adoption of the mediocre curriculum sequences used in a number of mid-performing states and promoted progressive instructional dogmas shared by its developers.”

These failed progressive instructional methods include “convoluted math strategies, group learning, and [emphasizing] how students get an answer rather than whether they get the right answer.”

Common Core has turned out to be an expensive disaster for America, with billions of tax dollars wasted on incentives for states to adopt the national standards, on developing and implementing new Common Core-aligned tests, and on ineffective curricula.

States should repeal their Common Core regimes and consider standards that actually produced higher student achievement, such as Massachusetts’ pre-Common Core standards. They should also give parents and their children greater school choice, so they are not tied to the regular top-down government school system.

Lance Izumi is senior director of the Center for Education at the Pacific Research Institute and author of the new book Choosing Diversity: How Charter Schools Promote Diverse Learning Models and Meet the Diverse Needs of Parents and Children.