Mesic said he was pleased that classes would not be attended only by Serb children but all children who so wished.
Asked to comment on the position of the Serbian Orthodox Church and other religious and ethnic communities in the country, Mesic said that Croatia had regulated this issue at the highest level, but that there were still problems as a result of the 1991-1995 war.
Describing the general situation in Croatia as good, the president said that attacks on returning Serb refugees bothered him and that their return was in the interests of the country because it showed the maturity of Croatian democracy and society.
"I expect the state authorities to identify those who harass people because that is harmful not only to individuals but also to the country which wants to join the European Union," he added.
Commenting on the Christmas message by the head of the Serb Orthodox Church, Patriarch Pavle, in which he called on Croatian authorities to protect Serb returnees, churches and clergy, Mesic said that the Croatian authorities were doing their best to punish any attack or act of harassment on religious or ethnic grounds.
"I expect that we will be much more effective than we have been so far," the president said.
The ceremony was attended by Serb Orthodox clergy and prominent members of the Serb Orthodox community in Zagreb.
Kantakuzina Katarina Brankovic Secondary School was founded in 1814 and closed in 1945. It resumed classes this year.