Good student don't have a specific stipulate .Everyone can be a good student.Some can get good grades,some can win prize in competition,some have a very strong presentation skill,they all good student.
Some teachers always judge their kids by grades.They think kids don't stuy hard when they don't get good grades.It'sthe wrong thought.
In the university ,the final grades are divided into two parts.One is the ordinary performance and another parts the test .So grades is just a way to find which student is good at study.
All in all,I think not only teacher but also parents do better not to judge your students or kids by their grades.Everyone has his or hersstrong suit.
Your attitude,not your grades ,will determine the height of life.