Every project has a first step. For Lernwunder it was a small app with an unassuming name: Zahlzerlegung (“number decomposition”). It’s our oldest app, and much of what now runs as a matter of course through all our apps we learned here first – some of it the hard way.
Why number decomposition of all things?
The choice of topic was no accident. Watch primary-school children doing arithmetic and you soon see where it’s decided: in part-whole understanding. A child who knows securely that 8 breaks into 5 and 3, or 6 and 2, has the tool to move beyond counting. A child who lacks it is often still counting on their fingers in year three.
The research here is unusually clear: weak part-whole understanding is regarded as one of the main causes of later difficulties in maths. So if you’re building a first app meant to genuinely make a difference, number decomposition is a good place to start.
Three lessons that shaped everything since
Building this first app, we arrived at three convictions that have echoed through every design decision since.
First: structure beats randomness. Quantities must never appear as a random pile. From the start we showed everything grouped in fives. That single decision proved itself so well that it now sits inside Noa, our upcoming maths app, just as much.
Second: mistakes must not punish. In early thinking, the reflex was to mark wrong answers with red flashing or an error sound. We deliberately decided against it. A child who is practising should feel safe, not caught out. A “wrong” result becomes a calm detour, not a small failure.
Third: practising means practising the right thing. An app that only sets random problems wastes a child’s time. Even Zahlzerlegung had adjustable difficulty levels and progress tracking, so that practice targets what’s still wobbly. From that idea grew Droptiply’s adaptive repetition system later on.
The start of a family
Zahlzerlegung is still in the App Store today, plain and focused. But its real impact lies in having become the blueprint. Grouping in fives, the gentle handling of mistakes, targeted rather than random practice – all of it was born here and now carries Droptiply, TinuTime and Noa.
Sometimes the most important app isn’t the biggest one, but the first one in which you work out what you actually believe.