Students would ultimately lose interest in high school if there was an additional year. Students would stop attending school and attendance records would be bad. This will lead to a ruined reputation and a decrease in being able to exceed to the next level of education. The students would not attend these programs if they lost interest in their education, which will be the result of an additional year to wait. All the benefits of having more extracurricular activities and community service would be lost.
A fifth year produces no benefit towards a higher education, if the year is lost. Students who were looking forwards to college would be held back to gain more credential rather than to learn. This would, once again, cause them to lose interest in school, and it would seem as if college was unattainable.
In conclusion, adding on another year of high school would cause the students to lose both focus and interest in school. This would lead to the loss of a year, plummeting attendance and reputation records, and, eventually, students dropping out of school. A fifth year of school would stop it. For the aforementioned reasons, high schools should not add an additional year.