Answer:
This is going to be specific to YOUR school, so unless the person answering this goes to YOUR school, you probably aren't going to good a good answer here.
For a letter, you can do something like this:
Dear Brother,
I think you should consider changing from (another school's name) to (your school's name.) One reason you should change schools is because my school has a great principal/teacher, (insert principal/teacher's name). Then tell a few good things about your principal/teacher, even if they are kind of made up.
Another reason you should make a move to (your school) is because we have a great (insert sport or extracurricular) program. Tell a few good things about the program.
I know you like (other school's name), but I think you would really love it here at (your school) because of our great principal/teacher, (their name) and because you love (extracurricular activity or sport) and our team/band/whatever is the best.
Love,
Your name
Step-by-step explanation: