If you want to know where a student has their greatest spelling problems or areas of difficulty, you can accurately identify these through an Oldenburg error analysis. OLFA is the only measurement tool that can validly analyze freely written texts (at least 350 words with a minimum of 50 errors). This instrument is backed by over 25 years of research experience. After many years of practical application of the Oldenburg error analysis, very good results have been achieved in the support and therapy of students with significant spelling difficulties. In the scientific Frankfurt study on dyslexia and spelling difficulties "On the Therapy of Spelling Weakness" (approved by the ethics committee), the effectiveness of OLFA-supported support and therapy was evaluated from 2012 to 2015.