I think 'acts_as_list' assumes you have a "position" column in your table (that it manages), and ordering is always by that column, no?
Rails is opinionated software. =)
And now that I say that, I see ...
http://api.rubyonrails.org/classes/ActiveRecord/Acts/List/ClassMethods.html#M000571
acts_as_list(options = {})
Configuration options are:
* column - specifies the column name to use for keeping the position integer (default: position)
There you go. (Although the example shows ":order" instead of ":column" as the option for that; might need to try both.)