Educational institutions today are prone to divide students into different learning groups according to various criteria including abilities or age. I believe competence level is reasonable for efficient and effective learning especially for teenagers.【开头宜短，对背景进行一两句的陈述】

Here comes the first reason that the knowledge should be imparted at the same pace. The similarity in study level reduces the disparity in teaching, which means teachers do not have to take those superior orinferior into account and therefore speed up or slow down for several times.【说理一般一到两句即可】I have been a high school English teacher where students were randomly grouped. It was always the case that during the class those lagged behind need multiple explanations while the other got higher marks turned impatient even stopped listening and sneaked off. Not only did they feel unsatisfied, I was also anxious about the rather slow mode. Even after a semester, I merely finished half of the teaching syllabus.【进行一个切合关键句的例子：注意例子的细节补充】Therefore, without distinctive gap, teachers are able to plan their materials according only one level. 

Apart from the instructors, this method is also favorable for students.We all know that peer pressure is the obstacle for many juveniles aged from 15 to 18, via which they would sometimes be demotivated. 【比上面的说理还简短】For example, my younger sister is always annoyed because of her classmate who is a faster learner. The totally new formula in mathematics only costs her 10 minutes to comprehend, but for my sister it would be 3 hours. Being deficient to her, hardly can my sister like the math class any more. If she were surrounded by the same level friends, she would not feelisolated but relaxed about the same speed they have. She would even be confident for further learning and thus the influence would be moredesirable. 【同样再抛一个有细节的例子】This accounts for why level difference is the priority for the sake of students’ learning. 

Although some opponents may argue that level-based class is biased, which looks down upon the laggard ones, what I need to clarify is that it, on the contrary, prevents the potential discrimination. The original division closes the door on poor learners in that they tend to be ignored by teachers, so does those perform better. The average level will be the standard resulting in the low efficient learning.【考虑到题的题型，因此在这里小小地进行一个让步反驳加强论述的充分性与补充字数】

In a nutshell, either for teachers or students, the class separated by teenagers’ level is beneficial.