Children need to be able to hear sounds, know their position in a word, and understand the role they play within a word. This Phonemic Awareness activity is not a letter sound-correspondence activity but basically for students to hear the sound that is the same at the beginning of a word. As children gain an understanding of these sounds you can begin to add the visual understanding of the letter as well.
As you introduce this activity to very low level students provide them with one board and the four corresponding beginning sounds that apply. As students become more proficient and understand and differentiate beginning from middle or end you may wish to add more boards as well as more card choices.