New York City parents are understandably nervous about tough new state tests that were rolled out last week. And some parents whose children have already taken the tests are outraged. They shouldn’t be: the tests, which measure math and English skills, are an essential part of rigorous education reforms known as Common Core that seek to improve reasoning skills and have been adopted by 45 states.

The city says that it provided adequate advance notice of the tests and that last year more than 90 percent of New York teachers said they understood the Common Core material. The outreach program could have been more aggressive. But with that proviso, New York deserves enormous credit for being one of the first states to carry out what is clearly the most important education reform in the country’s history.

The Common Core standards were the product of a heavily researched, bipartisan effort pioneered by the National Governors Association in collaboration with the Council of Chief State School Officers. The effort arose from a broad recognition that the United States was losing ground to many of its competitors abroad because the learning standards as applied in most states were pathetically weak. The problem came to light when students who sailed through weak state tests did significantly worse on the rigorous federally backed test known as the National Assessment of Educational Progress.

The Common Core standards do not call for a specific curriculum, reading list or anything like that. Rather, they lay out an ambitious set of goals for the math, reading and writing skills that children should acquire as they move through school.

The goals are internationally benchmarked, meaning they emulate the expectations found in high-performing systems abroad. The intention is to help students develop strong reasoning skills earlier than is now common.

The specific skills that students will be asked to demonstrate build in complexity from grade to grade. By fifth grade, for example, students will be required to produce essays in which they introduce, support and defend arguments, using specific facts and details. By 12th grade, they will be asked to solve problems and answer questions by conducting focused research projects — using skills that are generally associated today with the first year of college. To get students where they need to be, the states and localities will need to provide stronger teaching and course materials that are aligned with Common Core.

The standards are flexible so that states and localities can implement them in varying ways. But the whole point of the exercise is to replace the mediocre patchwork of learning standards that put American children at a distinct disadvantage when compared with their peers abroad.

The standards are fairly new, and shifting to them will cause some anguish, particularly among parents. Last year, Kentucky, the first state to adopt tests based on the Common Core system, found that the proportion of students who were rated “proficient” or better in math and reading dropped by about a third in both middle and elementary school the first time the new tests were given. That is likely to happen in state after state as weak tests are replaced by stronger ones.

There is a further challenge to Common Core from the political right. The Republican National Committee has attacked the standards, arguing that they usurp state authority. Last week the Alabama Legislature took up a bill that would roll back the standards.

But if the country retreats from the Common Core reforms, it will be surrendering the field to competitors that have already left it behind in math and science education, which are essential to participation in the 21st-century work force.