In my choir, I noticed that the sopranos tended towards /k/ whereas the altos towards /kw/. The tenors and basses varied. Singing together it all merged into a strong /kw/.
Why do some people say /kw/ and others /k/?
Well it’s probably because of the following vowel sound /ɔː/ which is made in a very similar position to a /w/ sound. The /w/ merges into the /ɔː/ and is lost. That’s why a native speaker might say /k/ for quarter, but will always say /kw/ with other vowel sounds like queen, quite, quote.
How do YOU pronounce quarter?
With /kw/ or just /k/ at the beginning? You might want to check similar words like quartet, quorum, quart, and Quorn (which you may or may not pronounce the same as corn).
Comment below and let me know!
You can listen to my choir sing the song here (at 0:53 you can hear quarters)
You can listen to Simon & Garfunkel sing the song here (at 0:53 you can hear quarters)