In my very distant view from across the pond, I have heard that they have dropped the O Levels and A Levels but I'm unsure what has replaced them. I, too, am totally clueless about the British system. But I have sort of gathered that O Levels and A Levels (and recently their replacement) indicates a completion of high school or its equivalent. In the States, a certain number of credits must be earned which usually takes four years. The fact that these credits have been earned is indicated by the awarding of a diploma in a graduation ceremony. In the UK, it seems (as I've seen many times) that [someone] got their A Levels or O Levels in [a subject] so they left school. Maybe it's better that they don't actually have a graduation ceremony as graduations have become very chaotic with sudden cheers or catcalls erupting as a certain person's name is called and entire groups rising up and departing as soon as their graduate has received his/her diploma.