The U.K. website "iPads In The Classroom" is specialized on iPad usage for students and teachers. The review site recommends Textkraft as one of the best writings apps and points out the great cost-benefit ratio.
The pro versions of Textkraft are great for students of all languages. The built-in dictionary provides corrections, similar words and synonyms while you write. This is a great tool for the next English essay, as for the French or Spanish lessons. Textkraft is available in German, English, French and Spanish.