If the norm in your circles is to have children in your teens, and you think that people who have qualifications are snobs or ‘other’ then it will be difficult not to follow suit. If all your friends and sisters have babies it’s natural to want one too.
After that it comes down to luck. If the father of your baby stays with you, if he has a job, and is supportive of you having a job, or getting qualified to get one, if you have supportive parents and are academically inclined then you are in with a chance.
Many aren’t though. I worked in an FE college years ago, in the days when they taught O and A levels to those without them. I came across numerous young women whose husbands/parters had no work and few prospects because of Thatcher’s decimation of industry. The women were trying to change things by getting qualifications that would lead to jobs, but often the men were very resistant- insecurity, jealousy, fear of further emasculation etc. Often other women would make life difficult too - the idea of someone ‘getting above themselves’ is very strong in some communities. It became very difficult for the women to do well if they struggled to get babysitters, were mocked for being ‘at school’ in their 20s etc. Many gave up, and those who didn’t often lost their marriages (think Educating Rita).
Cultural norms have a very strong grip. It’s no different from parents wanting their children to go to university and get ‘professional’ jobs afterwards - that’s a cultural norm too, when everyone around you wants the same for their children.
It’s all very well having people (whether they are teachers, social workers or health visitors) telling ‘them’ how to behave like ‘us’ and despairing when it falls on deaf ears. Darren McGarvey writes (and speaks) very well about this dichotomy- the middle classes trying to show the poor how to be like them but without realising that with both hands tied behind their backs it is much more difficult, and that’s if their clients want to change their culture and way of life in the first place. Many don’t, and the question should be whether that is necessarily or objectively ’wrong’.