In my district "honors" classes start at the junior high level. In 6-8th something labeled honors would be for gifted &/or high achieving kids.

At the high school you have to earn your way into the class. Ie.. get certain grades on per-requisites including 8th grade clases.

It depends on subject manner how they are different. But the one big difference is the honors classes have a lot more homework. In math for example, the same text book will be used. But the grade is bases more on testing, homework will often not be graded just checked for completion. And the teacher will assign more of the hard problems, expect the student to do what I call 2 or 3 step problems, and learn to write proofs. Science is similar. In English/Social Studies students are expected to be writing well without much help or direction, more complex texts are used, and more class time is spend on class disscusion rather than teacher lectures. An example of the text is that the 9th grade non-honors class read the Abridged version of Tale of Two Cities and the honors the regular one.

There are pro's and con's on the honors vs. non-honors classes. Basically those labeled "honors" are really prep for taking AP classes in 10th,11th, 12th. There is a LOT more homework in the honors classes at my school, but the homework is less busywork. The teachers expect that the honors kids can keep track of their homework, turn it in on time, and in general don't need a lot of babysitting.