Pretty good
1) I suggest that in each set of flash cards, a user can view a list of all the words. Or, when a category such as "learning" is pressed, the words with in it should be displayed.
2) The order in which flash cards appear is flawed; there are always words that keep coming up, yet some havent shown up at all.
3) Each words should have a few synonyms.
4) Instead of just having two options (know or do not know), there should be an intermediate choice for words that users sort of know. These words should be put in the "reviewing" category.
JAZegers about
SAT Flashcards: Prep & Vocab