The "End of the Year" dance is the dance that appeared in The Key, it appeared to be that only couples could go inside as in the background of a scene, Jim could be seen turning people away. None of the members of Team Lyoko went to the dance (even though Odd came close) due to the fact that they had to go to Lyoko to retrieve Aelita's memory fragment. The dance is not seen or spoken of again however it is possible that the prom in Teddygozilla could be the first dance however this point remains unclear.