12 words in a week might still be too many for someone who usually gets 0 on a test. Make sure they've got their own success chart where 1 right is a positive start. The first week will be all about thinking in sounds and moving the puzzle pieces to match the sounds, then copying the word in syllables and finally writing it out as a whole. If they're feeling confident, try one they like without puzzle pieces (i.e. spelling). Each week, pick the words that are most likely to succeed - the ones with the most single letter graphemes & clear syllables.
No more look/cover/write/check! Instead:
How many syllables?
Say them clearly. (put down puzzle pieces)
Build syllable by syllable/sound by sound.
Write syllables (copying is fine)
Write out whole word.
Identify the bits that need concentration.
Try it without puzzle pieces.