Secondary school students in Thailand's capital rallied Saturday for educational and political reforms, defying government threats to crack down with legal action against the country's high-profile protest movement.

The mass student-led rally that began Saturday was the largest in a series of protests this year, with thousands camping overnight at Sanam Luang field near the royal palace in Bangkok.

Organizers predicted that as many as 50,000 people would take part in the two-day protest in an area of Bangkok historically associated with political protests. A march is planned for Sunday.