Thousands of high school students have staged demonstrations in cities across Spain to protest over the country's education law, changes in the duration of university degrees and university fee hikes.

The protests Thursday were called by the Students Union, with the biggest marches taking place in Madrid, Barcelona and Valencia.

The demonstrations came at the end of a two-day strike by the students that had uneven support.

The education bill was brought in 2014 by the conservative Popular Party. Opposed by most other political parties and many teacher and parent groups, it increases the number of annual exams and reintroduced religion as a subject. The government claimed it was aimed at stemming Spain's school dropout rate.