The demonstration was held under the slogan "No to chaos in education" and marched through central Warsaw to the Presidential Palace and later to the parliament building.
At the Presidential Palace, the protestors left a petition urging the president to veto the education reform bill.
Later the protesters piled a heap of chalk in front of the parliament building to symbolise "broken educational and professional careers".
Five opposition parties declared their support for the Saturday demonstration.
The organisers said the demonstration attracted about 50,000 protesters, while police estimations put the figure at up to 15,000 at the start of the demonstration.
Currently, children in Poland attend to a six-year primary school, which is followed by a three-year lower secondary school and a three year upper secondary school ending in Matura, or the final exams required to continue education at university level.
The reform foresees the reintroduction of an eight-year elementary and four-year secondary school. (PAP)
jd/