Some children do better in school than others for many reasons. All kids have different talents and abilities, and some of these just show up better in school. Some children may be naturally better at reading and writing, working with numbers, and at storing and using information.
Some children are very organized, good with managing their time, and diligent about doing their homework. Most schoolwork requires these skills, so kids who are strong in these areas are likely to be better students. Still, most kids have enough ability to earn the basic skills taught in schools, things that they will need to know to get along well in the world once they graduate. Kids succeed by putting a lot of time and effort into their studies, by getting help when they need it, and by not giving up!