Because the "Harmony" curriculum uses non-standard methods (especially in Russian grammar and math logic), parents often use GDZ sites like Gdz.ru or Euroki not just for answers, but to understand the logic the program expects from the student.
These workbooks are part of the "Harmony" UMC, primarily supporting textbooks like "To the Secrets of Our Language" (Russian) and Istomina's "Mathematics".
They contain training exercises designed to improve orthographic and grammatical skills, as well as problem-solving logic and "educational independence".