&lt;p&gt;You need to create as many \&quot;groups\&quot; as participation sessions you plan to organize for each level. For example, if students from the same class participate at two different times, that's two groups. If you want two classes of different levels to participate at the same time, that's two groups. If you organize a training on a 2012 contest before the real contest, you will need groups for the training, and different groups for the contest.