Workbooks for kids have been the same for such a long time. Books titled “for kids ages 4-7 or 7-10” can be found anywhere and even become best sellers. Nevertheless, it is scientifically proven that every child grows significantly every year and kids of different ages are not alike. A high-quality book cannot fit second graders and fourth graders at the same time. Forced to learn with an unsuitable book, kids may start to get bored, waste their time and lose their interest in studying.