Kids that are in Middle school should write and express their feelings in a journal because there are many benefits for it. For example, some benefits are that writing in a journal can improve writing skills, can express their thoughts meaningfully, and also many more benefits too ("The Benefits of Journaling for Kids"). If you don't want to write in a journal about your feelings and what's going on in your life, then you can also write about math, nature, history, vacationing, and also a lot more things
It's sort of obvious that journaling can improve your writing skills because if you write in a journal, you probably write in it often and becuse of that you will improve many writing skills. According to the article "7 Benefits of Journaling for Kids"