The overall class scores will be calculated based on the total class average. This means that a class could still win the contest if their overall average class score is higher compared to the class who had a higher daily average.
This can happen if a class had most of the students playing in the contest at the start and the students reaching the 1,000 question limit earlier on. That class would therefore have a higher total score earlier in the week compared to later in the week as most of their point would have been earned then.
It could also be that a class had started earlier in the week but for some reason was not able to play during the week, thus not appearing on the Daily winners list. That class however started playing again toward the end and achieved higher scores.
To get the best understanding of where your class is in the leader board, we would advise that you look at the Top 10 classes leader board. As the score will be based on the total class average.
Note: The contest leader boards are not live and will be updated every 30 minutes - 40 minutes.