A simple answer marks the very core of the WW model. Consistently offered and just for writing. Every day teachers present a math lesson. First graders learn to count and practice it every day. Every year new skills are added and drills and flashcards reinforce the learning on a daily basis.
Reading is handled in much the same way.
Letters, phonics, and words are imploded on children in K-I throughout their day. Special time is held sacred as teachers work each day to encourage improved letter recognition and reading. Literacy depends on a student's ability to read. Writing begins as students learn to form letters and place them carefully into words. Once basic skills are in place, writing expands into other content areas.