I have not been able to locate any research showing that worksheets or drills carry over into students' successful application of skills in authentic reading/writing contexts. In fact, decades of research show that drills do not improve student writing. Much like passing the Friday spelling test, students can perform the skill in isolation, but they don't apply it in the course of daily writing and reading.
She goes on to explain that the skill we want students to master islearned best in the context of a meaningful piece of writing where the student can see how the skill being taught makes the writing clearer and more understandable to the reader. Food for thought as we consider purchasing a truckload of workbooks for our literacy program.