Police arrested 10 protesters and detained 55 people in central Athens on Friday morning during a rally commemorating 15-year-old Alexis Grigoropoulos, who was shot dead by a police officer in the Exarchia district on December 6, 2008.
According to reports, the march was attended by more than 2,000 schoolchildren and students.
Riot police came under attack by a group of protesters and reportedly used tear gas to disperse them.
A second rally by leftist organizations and self-styled anarchists took place in the evening.
Police officers later clashed with anarchists in Exarchia.