I think it is worth noting that "Moja szkoła to liceum" makes much more sense in Polish than " My school is a high school." in English.
Your high school equivalent in Poland does not have to be
liceum - the school that prepares to higher education ,
you can choose technikum or liceum zawodowe - which prepare you for work but also provide you with enough knowledge to take Matura exam, and higher education in the field you chose, but it is year longer than liceum
you can also choose "szkoła zawodowa", which prepares you for work. It is schorter than Liceum, you leave with some skills, and often a possibility of taking journeyman exams. You need to take two years of "liceum for adults" to pursue higher education.
So a kid telling you her school is "liceum" is not only telling you she is old enough to go to high school, she is also boasting that her school is "liceum".
Well, that sure sounds like "gimnazjum"... even if, from what I see, it is rather "liceum" indeed. We try to accept the equivalents from English-speaking countries (as you answer in English, after all), but Germany/Sweden really seems too much.
Frankly, I think that accepting too many alternatives is more harmful than helfpul anyway. Personally I'd recommend just treating szkoła podstawowa/gimnazjum/liceum as primary school/middle school/high school and not going too deep into the different education systems :)
Not really. These days "grammar schools" in the UK are just the state secondary schools that select by ability.
In the 1950s and 1960s "grammar schools" in the UK were roughly equivalent to a "liceum", but they've been phased out and since the 1980s, only about 5% of UK secondary schools are "grammar schools" now. See also http://www.bbc.co.uk/news/education-34538222