SwiftKey Note (free) was just released and in this iOS version (universal) provides the writer with a standard keyboard and 3 word prediction choices above the keyboard as well as intelligent auto correct. Word prediction is a great option for students who struggle with spelling. SwiftKey is quick and integrates with your Evernote account seamlessly. Notes can be inserted into your currently existing notebooks and tagged.
In addition, SwiftKey reported adaptive learning based on words you frequently use. It would be interesting to test out with student and see how good this works for phonemic spellers. Also, analytics are available within the app to let you know how much support was used. Interesting data for teachers.
Although this app does not come with auditory feedback for words and sentences, the built in speech to text accessibility feature works great.
Currently there are multiple apps (iWordQ and Co:Writer) that help struggling spellers with word prediction skills however these apps range in pricing from $17 to $25. It would be interesting to see if this app can support learners as well?