Thousands took part in the rally which the Bad Student group organisers hashtagged #ByeBye Dinosaurs.
The peaceful protest was the first major gathering since Prime Minister Prayuth Chan-ocha said on Thursday (November 19) said that police would use all laws against protesters, who have become the biggest challenge to the establishment in years.
Protests since July have three core demands: the removal of former junta leader Prayuth as prime minister, a new constitution and reforms to the monarchy of King Maha Vajiralongkorn.
But the high school students also seek greater freedom and fairer treatment within an education system they say is archaic and aimed primarily at inculcating obedience. Many spoke of the importance of gender equality.
Another major protest is planned at the Crown Property Bureau on Wednesday (November 25). Protesters say they seek to reclaim the palace fortune, which the king has taken under his personal control.