I think the reason for this is that it is only select chapters from "Up from Slavery" in our book. It starts with the first 2 headings being

chapter I. A Slave among Slaves. and Chapter II. Boyhood Days then skips ahead to Chapter XIV. The Atlanta Exposition Address. You're right

though, I would have liked to learned more about his education process as well

That right there is one of the biggest annoyances of anthologies. They cut with impunity sometimes.