Nhờ sửa bài giúp

First, it is better I test twice, so do I need to know the names of students when they fill out a questionnaire or do fitness tests for determining the progress/ decline percentage.

Or the comparison is generally, means I take a test twice from a specific group of students without knowing their names.

And in general, this particular group will be compared in two stages, not individually.

Second, now is the second semester, it is the middle of the academic year, and I want to test on the samples twice.

I can not collect data from 15 age students in the first stage of data collection because they will change their school in the new academic year.

I mean, in the first phase, I will work on 13- and 14-year-old students, and in the second phase, this group will go one year higher and will be 14 and 15 years old.

Is there no problem?

Third, there are 19 districts for the Ministry of Education in Tehran.

For example, for 300 students, I will select 15 districts, and then I will select 5 schools in this district, and after, I will select 6 classrooms in each school, and 10 students from each classroom?

For example, I choose three schools in a rich district at random, 5 classrooms from each school, 10 students from each class, and the same in the poor district?