o (u), Vowels saying their name,
y(eye), ow(o-e), ew, oy
By now there will be many flashcards in the pile and you may feel that the student is getting 'tired' of such a big pile. The remedy is to reduce the pile. Do a test one day. Lay on one pile the ones they know well and on another pile the ones that still need practice, including any new ones. Just practice this pile. You can always bring out an old one if needed for extra reinforcement.