Iranian students have defied a security clampdown to stage anti-government protests throughout the country, witnesses and opposition groups say.
Unconfirmed reports say about a dozen people have been arrested, including at Tehran University in the capital.
Last year's protests led to clashes with security forces as students lashed out over the disputed re-election of President Mahmoud Ahmadinejad.
This year's protests appear smaller, and there are no reports of violence.
Pro-government rallies have also been held across the country.
The annual protests are held on Student Day, Iran's annual commemoration of the killings of three students during anti-American protests in 1953.
In recent years, students have used the 7 December anniversary - known locally as 16 Azar - to demand greater political freedom.
Leaked mobile footage from campuses in several Iranian cities, including Tehran, Ghazvin and Tabriz, showed students chanting anti-government slogans and singing protest songs.
Opposition leader Mehdi Karroubi is reported to have met the families of jailed student activists and condemned the authorities' attempts to stifle freedom of expression.
The Iranian authorities arrested thousands of people during the mass street protests that followed the 2009 election that returned President Ahmadinejad to power, amid opposition claims of widespread fraud.
More than 80 have been sentenced to prison terms under Iran's security laws.