Hello Quoofeeyoomb29
When travelling with Day Passes for Schools, the cost is a fixed flat rate, you will automatically get reserved seats on IC and IR trains. This is why you have to book the tickets in advance; you travel with discounted tickets, therefore you have to commit yourself to a predefined itinerary which helps the train companies to plan their rolling stock accordingly.
If you want the full flexibility without preannouncement, you must stick with Day Passes for Children (6-15.99 years of age), Friends Day Passes for Youth, or regular tickets such as Saver Day Passes or Point-to-Point tickets; they all allow flexible travel on all public transit services.
Kind regards,
Roland