While Shmoop always warns against naming the poet as the speaker, in this case, we think it's a safe bet. After all, this poem was written in a letter to his son, and he practically signs it at the end with that "S.T. Coleridge." So that' makes our job pretty darn easy.
It's worth learning a bit about Coleridge himself to understand just where he's coming from in this poem. Why write a lesson in meter to his seven-year-old son in the first place? Let's hear from the poet himself:
As far as meter acts in and for itself, it tends to increase the vivacity and susceptibility both of the general feelings and of the attention. (Source.)
When you get down to it, that's just a really fancy way of saying that meter makes for vivacious, attention-grabbing poems. And who wouldn't want to write those?
So if our poet wants his son to be a poet, too, it makes sense he would want his son to learn meter, and that's the most important thing we can remember about our speaker; he's a poet and a loving father, and he wants to share his passion with his son.