One possible version:

Dear Jack,

     Your letter has reached me already. In your letter, you said you wanted to know something about our class.

Now let me tell you.

     On the whole all the students are doing a very good job. More than 70% of them have formed a very good

habit of studying and concentrate on learning their lessons. Besides, they are good at communicating with the

teachers and other classmates, and are always willing to help others. Every time they take an examination, they

get excellent marks.

     However, there are also some problems. So far, some of the students still haven't formed effective ways of

studying. As a result, their grades are not satisfactory. Also, a small number of students don't work hard. What's

worse, some of them are addicted to the Internet games, and even often go to the Internet bars.

     In my opinion, as students, we are pressed for time. Every minute should be made use of to study our

lessons. Of course, health is also important, so we should spare some time to take exercise to keep fit.

     Best wishes.

                                                                                                                                                    Yours,

                                                                                                                                                     Li Hua