The exam is not for high school students, 8th grade students, etc.
It is an exam for graduating from a teacher’s school.
Of course, teachers today couldn’t pass that test, so it is still very telling.
Laura Ingalls Wilder passed the teaching exam at 14.
In 1895, and for many years after, graduating from eighth grade represented the extent of many students’ public school education.
The point was that students with an 8th grade education were prepared to function in society. They could communicate, correspond, calculate, and knew how to handle any income they generated.