Developed by Dr Claus Zinn

Computer Scientist and Educational Researcher

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Lehrer Lämpel

Version 1.0
Lehrer Lämpel: Addition and Subtraction of Fractions
An educational app that supports school kids to train their fractions skills (addition and subtraction).
  • Practising addition and subtraction of fractions
  • With 1 or 2 digit numbers
  • With two denominator policies: lo
    • lowest common divisor
    • any multiple common divisor
  • Worksheet with predefined tasks
  • Unlimited number of (randomised) exercises
  • Support for self-defined tasks
  • Direct feedback for correct/incorrect steps
  • Intelligent next-step help and error correction
  • Multi-lingual help page (english, german, french)
  • Available for iPad tablets, from iOS7
  • Price: .99 USD, 1.09 Euro
Compatible with the iPad. Requires iOS7 or later. No WiFi, Edge, or 3G network connection required. No ads.


Lehrer Lämpel: Fractions is an educational app that supports school children (usally 5th grade) to practise their skills to subtract or add fractions.

Easy input of numbers to the blackboard.

Pupils can ask Lehrer Lämpel for help at any time. Help first signals an erroneously learner step; if there are no errors, a single hint towards the next step of the solution is given.

All teacher steps towards the solution are followed-up with a step explanation as well.

When adding/subtracting fractions, two policies can be followed: least common multiple, or any common multiple.

Supports self-defined tasks and there is a work-sheet, and randomised exercises

Supports English, French and German.

Available on the iPad, for iOS7 or later.


Version 1.0

Released on November 19th, 2014
  • NEWInitial Release.


Privacy Policy

Our privacy policy is rather simple. We do not collect any information from you and your child when using our app or browsing our website.

You or your child will never be prompted to provide any sort of information in our app. You are free to use the contact form on the website to give us your feedback, ask questions, elicit new app features, or file a bug report. For this, you can equally contact us at

We will use your contact information only for being able to reply to your requests. It will not be shared with anybody else.

Our app is solely financed by its price tag, there are no in-app purchases, and the app is ads-free.


Contact Us

Please use the following form for questions, feedback, feature requests etc.

Our email:

Postal Address

Dr. Claus Zinn, Diplom-Informatiker (Univ.)
In der Gebhardsoesch 33
78467 Konstanz, Germany