pronunciation - How do students respond to the "roll call" and how do you pronounce it?

I have two questions.

In the UK, to do (or is it read?) a roll call is commonly referred to as "calling out the register". It's been so long since I was a child that I'm not absolutely sure how students responded. I think it was "Present, miss/sir"

I also seem to remember students just raising their hands. Are there different responses in the rest of the English speaking world?

Secondly, I am experiencing difficulty in pronouncing roll call. I can say each word separately without any trouble but when I join the two together it sounds as if I'm saying "rolkol"; "rolekol" or "rol kol" I've looked in wiktionary and TFD but neither have the pronunciation. Should I pronounce roll in "roll call" as /rəʊl/ or /roʊl/?

EDIT

It seems responding to the roll call with "present" has become dated both in the UK and the US whether it holds true for Canada and Australia is unknown. Apparently, British students responded with "Yes, miss/sir" until the 70s but now the simple, "Here" is heard on both sides of the Atlantic. The Longman Contemporary English Dictionary, claims that call/take the register is old fashioned in the UK, but I wonder if that really is the case, and whether in the US "calling the roll" is becoming dated as suggested by the Google Ngram chart in @bib's answer.

Answer

In the US, the most common answer is Here. While Present was also heard in the 1950s and earlier, this has largely disappeared except in smug exaggeration.

There are slight variances in regions across the US with a more significant oh (as in bowl) heard in the Northeast, and less so in the Midwest.

SUPPLEMENT: Calling the roll was used in schools through the late 20th century, and roll call is still used in the military and uniformed services, such as fire and police, and in legislative bodies (as in a roll call vote). Since the 1980s, the phrase taking attendance has become more common, as reflected in this ngram.