When creating new sessions, they are generally related in some way to sessions that already exist.  Session order is almost never going to be the same as, for example, alphabetical order.  So, to give the most flexibility each session has a sequence value that indicates its relationship to the existing sessions.

Here's an example of a broken session list:

As you can see, we sorted the list by Sequence and both Fall and Late Fall come after July, which is clearly incorrect.  This produces a graph like the following:

This shows that the values for Fall are much closer to the September values.  The relationship of the months to the seasonal Fall session in this case is probably September-October, but in your district it could be as late as December, so the sequence values need to match your expectations.  Here we changed the numbering to indicate where the sessions might fall:

This changes the graph to the following:

Note that the sequence numbers may contain gaps and duplication, as long as they are in the relative order.  If there is duplication it means you only care that those sessions appear together but you don't care in which order they will appear (they will still be consistent in their order, as they are secondarily ordered by when the session was created). Here is an alternate sequence order:

Here you can see that we left plenty of room between sessions for the addition of seasonal or other special-purpose sessions.  This ordering produces the following graph (which is only slightly different from the previous due to moving Fall before September):