I know that some single-syllable words (most pronouns, for example) come in two varieties, with and without an accent mark on the vowel.
"Él" has a different meaning than "el", but is it pronounced any differently?
Generally there is no difference in the pronunciation, sometimes it could be a difference in the stress, the pronoun would never be used as a "weak form" or contracted.
"No iremos porque (e)l niño no quiere ir" The bracketed "e" could be elided. "No iremos porque él no quiere ir" The final "e" in porque and the inital "e" in él would be both pronounced.
Generally speaking, when you have a diacritic accent, its role is solely to mark the grammatical function of the word, and does not have any influence with the stress of that word.
The stress, as @Laura already stated, depends only on the type of word, so:
el
) will be elided but a pronoun (él
) won'tmi
) would be elided but a declined pronoun (mí
) won'teste
) would be elided but a pronoun (éste
) won't.In the case of Él, there is a pause before it. If you were to break it down into syllables,
No iremos porque él no quiere ir
No/y/re/mos/por/k/el/no/kyeh/re/ir
You'll notice that the "el" part is its own syllable.
No iremos porque el niño no quiere ir
No/y/re/mos/por/kel/nin/yo/no/kyeh/re/ir
In this one, you'll see that the last syllable of "porque" is merged with el. Ending up with something that sounds like "porquél"