To answer your question: Your A levels would be considered high school in North American and is still considered basic education, not necessarily college prep, although the courses one takes in high school can be college prep or trade prep or neither. They would all obtain the same diploma The higher education that the society is ranting against is university degrees.
Youths can drop out of high school at age 15 here in Canada, after what would be considered junior high school. This is highly looked down upon here and disqualifies one for almost any jobs, even entry level, unskilled jobs. Cleaning and other physical, unskilled laborers would be the most that is open to someone without high school diploma.
At one time, in the 1970's youths could drop out of high school at age 15 and enter an apprenticeship, trade or get an unskilled job. Many witness families did encourage their kids to drop out, get menial jobs, and pioneer. Many collected welfare or unemployment insurance and pioneered which became quite an embarrassment to the society a few years later when the rules for collecting such benefits were severely limited to prevent such abuses. After that point, JW children were not encouraged to drop out of high school (your A levels) but to finish so they could at least support themselves.
A few years later, it was even recognized that higher education was needed for many jobs that in the past were not required. So, the social sanctions were lightened up a bit, but, because the society found that almost everyone who attends college leaves the organization, they have gone back to their former hard line stance against college/university.
Nowadays, every skilled trade in Canada requires high school completion to enter. Even McDonald's expects youths to be attending school before they will be hired part time.