Common Core is the latest attempt to standardize what students need to know. The Common Core curriculum is designed to ensure that students across the United States are experiencing the same rigor. In this, Common Cores seeks to present "a consistent, clear understanding of what students are expected to learn." Common Core has been touted as being constructed by people who are involved in education. Therefore, education professionals have come to an agreement as what students are "expected to know" at specific grade levels. Common Core removes the guesswork for new teachers and parents as to what needs to be taught. The ability to standardize learning outcomes and expectations helps to ensure that all students receive a similar educational experience.
Proponents of Common Core point to its rigor as being fundamentally different than what was previously featured under No Child Left Behind. In previous high stakes, objective assessment, teachers felt rushed to teach many standards to students, without being able to engage the curriculum in an indepth manner. Coverage came at the cost of thoughtful analysis. In Common Core, there are fewer standards, but the expectation is to be able to address them in an indepth and thorough manner. Common Core's depth is a point that its proponents use in its defense.
Additionally, an added attribute to Common Core's rigor and depth is the honing of students' critical thinking skills. Since Common Core focuses on content in a detailed and thorough manner, students can engage with the standards in writing that probes into justification and argumentation. Researchers who support Common Core point to the fact that students need to be "college ready." An essential part to college readiness is the ability to think critically, justify one's thoughts through understanding text independent questions, and developing an argument through writing. Common Core speaks to this and proponents of Common Core argue that it will enable students to be ready for college and higher education in a more demonstrative fashion.
Common core is a curriculum that is taking hold in a fast growing number of states. The curriculum requires more analytical answers and critical thinking than most academic curriculums. It also sets benchmarks of what students should know by the time they finish a certain grade. This is supposed to discourage "teaching to the test," as you can't "teach to the test" critical thinking, and having benchmarks is in line with NCLB.
Common core is hotly opposed in some states though. Some parents and teachers perceive a "government takeover" as it makes all states that adopt it have the same curricula for each grade. (How this is a bad thing, I don't know). Some were opposed to NCLB from the start, and so oppose Common Core's furtherance of NCLB goals. Some even fear that the standards are somehow "too high" and their children will not pass the tests (How is rooting out grade inflation a bad thing?).