I seriously don't know where you take this from
'Until the 1990s, the majority of secondary school students attended various types of vocational education institutions, while access to higher education was limited to a relatively small group'.
(Maciej Jakubowski, Evidence Institute, University of Warsaw,January 2015)
'Young people of the working class were led into a cultural cul-de-sac,namely basic vocational schools'
(Rafał Piwowarski, Secondary Education in Poland, Council of Europe Press,1996)
You can read the same in stacks of scholarly research articles, books etc. Students who attended vocational schools did not get the chance to take the Matura exam which permitted access to higher education. The fact is that Communism did not provide equal educational opportunties to all children. And there is simply no doubt that a well connected family with Party associations could see to it that their child attended university even if that child was below average, whilst a brighter child from a working class family might well be denied the opportunity even to receive a full secondary education. The Communist education system focused on fitting people into jobs and that was all. If they were short of welders you were going to be a welder, if they were short of doctors you were going to train as a doctor and so on. Now, I'm actually not at all in favour of the American idea that everyone needs a college education. I also don't agree with turning every blessed thing into a college degree and trying to make it an academic subject but under the old system, there's no doubt that young people with potential slipped through the net.
my mom attended a weekend school that would end up in a matura if she didn't quit - she first finished a vocational school
If your mother was capable of taking the Matura, what was she doing in a vocational school in the first place? Do you see the unfairness and elitism of a system which decided that your mother should be denied access to a full education? Your mother should have received a proper secondary education on equal terms with every other child, and following Matura had a choice of university or an apprenticeship or technical qualification or just a plain old job. Did your mother receive her weekend school for free? I'm just interested because I would certainly expect that in a Communist country. Access to weekend schools would also have been limited depending on where in Poland one lived. A bright young person living in a rural area, who was denied the opportunity to take Matura at secondary level, might never have been able to get that chance in later life.
junk diplomas
That's a separate issue. It's a result of an improperly regulated higher education system.