Education system

Often, we heard about how they set up the syllabus of studies and how they conduct their own courses based on certain standard. That's fine.
What I dun like about the system is where they want to mixed between good and bad students. Their aim was to make used of the capability of the good student and hopefully, they can help those poor one in their studies and influence them so that they can be improved as well. However, things always don't work like what you aim to be.
The final result :
1.Good student's result maybe affected due to extra time needed to help out those weak one.
2.They might be learned all those bad things from the bad student.
3.Both of them will be good student.

Among all those possible consequences above, the chance for the third possibility to be happened is almost zero. Only good student maybe affected by them and need extra time to do extra work which is undesired.