Good students are interdependent. They ask for and give help. They look for detailed feedback on their work. There are some students who just can't learn. Some students just don't have what it takes.
All students can improve, even in their areas of weakness.
Good teachers don't give up on students. Students who don't succeed in school need a dose of the hard reality that awaits them in the real world. Students who do poorly in school would be more successful if they were more motivated. Students who do poorly in school would be more motivated if they had more success. For a listing of the most commonly requested modifications, take a look at our Teaching Methods That Work page.