org-agenda-scheduled-leaders

org-agenda-scheduled-leaders is a variable defined in `org-agenda.el'.
Its value is

("Scheduled: " "Sched.%2dx: ")

Documentation:
Text preceding scheduled items in the agenda view.
This is a list with two strings. The first applies when the item is
scheduled on the current day. The second applies when it has been scheduled
previously, it may contain a %d indicating that this is the nth time that
this item is scheduled, due to automatic rescheduling of unfinished items
for the following day. So this number is one larger than the number of days
that passed since this item was scheduled first.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.4 of Emacs.