Alliteration is when the initial consonant sound is repeated over and over. For example, think of all of your classic tongue-twisters (Peter Picked a Peck of Pickled Peppers); it is the "p" noise that is repeated over and over here. In "Mother to Son," I don't seen any good examples of alliteration. To be a good example, it would need to be several words, right after each other, at least in the same line. That doesn't really happen.
For rhyme, look to the third and seventh lines (stair/bare). The strongest of the three techniques is the rhythm. Read it out loud--it has a definite lilt and lyrical quality to it. The repetition, short phrases, dialect and metaphorical content all make the poem seem like a song or a nursery rhyme that a mother is singing to her son.
I hope that those thoughts helped; good luck!