The high-profile court case comes as Prime Minister Recep Tayyip Erdogan battles his biggest crisis in 11 years in power, which has hit the economy and is threatening the strongman's presidential ambitions.
Some 2,000 riot police were deployed in the central city of Kayseri for the start of the trial, roads around the courthouse were blocked and demonstrations banned for "security" reasons.
Activists trying to get to Kayseri for the trial said that several buses carrying demonstrators were prevented from entering the city overnight and this morning.
The attack was recorded by security cameras and the 19-year-old student, wearing a "World Peace" T-shirt, suffered a brain haemorrhage and died after 38 days in a coma.
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Eight men, including four plain-clothes policemen, are accused of premeditated murder and face life in jail if convicted.
In an attempt to avoid fresh trouble, authorities moved the trial some 550 kilometres east of Eskisehir to Kayseri.
More than 8,000 people were injured, the Turkish Medical Association says, during the protests in June that began as a peaceful sit-in against plans to build on a Istanbul park.
Erdogan called the demonstrators "vandals" and branded Twitter, used to organise protests, a "troublemaker". Heavy-handed police tools included tear gas, plastic bullets and even live ammunition.
Amnesty International said there were "gross human rights violations" and German Chancellor Angela Merkel at the time called the police response "much too harsh".