Let me give you my perspective as a high school math teacher who teaches incoming migrants, many of whom have had very little formal education.
The point of education is NOT that you will use these skills regularly. Some of them certainly might if they go to university. There are also foundational skills you learn, such as reading and basic mathematics. However, the most important benefit is that school teaches you to how to think. Things such as pattern recognition, how to interpret directions and follow them, how to stay focused on a task, how to analyze information and draw conclusions. These are the arguably the most important skills you are improving while at school. The subjects are the medium through which these skills are acquired. Without formal education, most students do not develop even beginner levels of these skills, and the more complex/abstract topics in high school develop these skills to an even higher degree. Let me give examples of two types of students I had this past year:
One type are those who have attended school through what I figure to be about 4/6th grade - they know the basic 4 operations, some know PEMDAS, generally fractions are a no-go. While difficult to work with this base knowledge in Algebra, it should be doable; most of algebra is about applying arithmetic with variables. However, the amount of difficulties with things such as not recognizing the pattern in how to plot coordinate points, not recognizing how coordinate points are written in tables, not recognizing visual and numerical patterns (think rate of change, increasing numbers of shapes, etc) - the pattern recognitions skills are abysmal and the ability to generalize patterns to the future or different situations is almost completely absent. For these students, it took them months just to understand how to substitute a value for a variable, despite knowing basic arithmetic.
cont.