1. Selection method: Top classes usually select outstanding students through selection tests or competition results, while key classes are usually selected through students' senior high school entrance examination results or school comprehensive evaluation.

2. Selection criteria: the selection criteria for top classes are students' intelligence, academic ability, creativity or comprehensive performance, while the selection criteria for key classes are students' comprehensive performance, academic performance or specialty.

3. Education methods: The education methods of top classes often pay more attention to heuristic teaching, research-based learning and the cultivation of innovative ability, while the education methods of key classes often pay more attention to exam-oriented education and the cultivation of basic knowledge and skills.