Knowji vocabulary apps are available for ipad and iphone. There are several different grade levels , and many are common core aligned. The apps contain lists of vocabulary words as well as easy-to-understand definitions, illustrations, and audio pronunciations. The practice sessions use a “spaced repetition algorithm” that reportedly helps to commit the word to long-term memory, and there is even a record function that allows students to record their own pronunciations and have them evaluated for accuracy.

http://www.knowji.com