The event was opened by George Reid, the Scottish Parliament's Presiding Officer, organised by the Hansard Society Scotland and supported by the Electoral Commission.
The "mock electorate" voted for their favourite candidate with the single transferable vote (STV), which is being used for the first time in Scotland at this year's local government elections.
Gordon Lawrie, head of modern studies at Portobello, said the vote was nearly split by the Independent "Save Meadowbank Stadium" candidate:
"Although they are all of different abilities, I would expect every pupil in S5-6 to get their heads round the STV. The difference would be that the more able ones could spot the weaknesses in the system that nobody admits to, for example, the difference between the large multi-member and small multi-member constituencies. A good Higher kid would be able to say there is a slight party bias in the way the system works."
The results of all the mock elections across schools in Scotland will be collated and the winning party will be announced in May.