NCLB stands for No Child Left Behind. It was a law in the United States that said all kids in schools must do well in their tests, especially in reading and math.
The law wanted to make sure that all kids, even the ones who were struggling with school, got the help they needed so they didn't fall behind.
To make sure this happened, NCLB made schools give tests to all students in the school. These tests were supposed to show if the kids were learning and if the teachers were teaching them well enough.
If the school had too many students who were not doing well on the tests, the school would have to make changes to their teaching methods or get help from experts to improve.
Overall, the goal of NCLB was to make sure that every child in America could read and do math at their grade level.