Abstract
Some school students can use taught knowledge in new contexts, while others although familiar with the taught algorithms are not able to apply their knowledge in new contexts. The main focus of the chapter is consideration of these inter-personal differences as an effect of the teachers' didactical variability in the domain of word problems.
Students of teachers with weak didactical variability in the domain of word problems are strong in standard problems, while those of teachers with advanced didactical variability may be weaker in them but better performing when solving non-standard, non-algorithmic problems. The crucial question is how to increase teachers' didactical variability.