These two poems have a couple things in common when it comes to poetic elements. First, structurally, these poems are similar. Neither is written in free verse. Both are made up of four stanzas of the same number of lines (although "If" has 8 lines each and "Road" has only 5 lines). Both have a rhyme scheme. Both employ non-rhyming sound repetition as well ("If" the word you; "Road" the words I and and).
If you look a little deeper, you will also note that both poems are built on metaphors. "If" employs several small metaphors in each stanza as points of comparison for growing up and tackling lifes problems. "The Road Not Taken" is built on one extended metaphor (Two roads diverging in a wood) as a point of comparison for life decisions.
The subjects of both poems can be related to life and growing up. I think the differences certainly outweigh the similarities in these selections, but I can see where a teacher might pair them on the basis of structure and broad subject matter.