This law has influenced schools to do much more standardized testing and to be much more focused on the results of those tests than they once were. The NCLB law has serious consequences for schools that do not make "adequate yearly progress" on their test scores. This means that the schools have strong incentives to have their students do well on the tests. This has led to many new practices that focus on the tests to the exclusion of other things. There is "teaching to the test," of course. There are also schools where classes that do not contribute to passing the tests (like PE) get cut. There are even many instances of teachers and/or administrators cheating to improve their students' scores.
Overall, the impact of this law has been to cause schools to focus on standardized testing in ways that many educators think is unwise.