Hi, Yes it shall affect your academic performance in school. Though it varies in universities abroad as all have their own parameters. One has to aim for high grades in school specially class 10th, 12th. Apart from this partcipation in some extracurricular activities in the school or even outside shall help you to build up interesting profile. If you can get recognition from some sort of national or international competition (esp. international olympiad or international research competition), that will help your chances a lot. So this is how much it matters.