Each chapter of The Story of the World Activity Books includes a set of "Questions for Review" to guide a discussion between the parent and the student and assess student comprehension of the text.
Some parents and teachers used the discussion questions with older students and painstakingly typed out the discussion questions and leaving answer spaces so the students could independently write their answers. As a response to customer requests, we created the Review Questions Worksheets (formerly known as the Written Comprehension Responses) to save parents and teachers time and work.
The PDF document states each review question and leaves space for the student to write a response.
Until 4th grade, we recommend a discussion between parents/teachers and their grammar stage students. Older students can work with greater independence, and write their answers on their own paper or in the Review Questions Worksheets.
The PDF is an optional supplement to the Activity Book. It does not replace the Activity Book; the answers are included in the instructor portion of the Activity Book, but are not included with the Review Questions Worksheets PDF.
The short answer: Review Questions Worksheets are intended for a subset of our customers. Adding the pages to the Activity Books would raise the cost of production and shipping for everyone. We made the PDF so interested customers could get the supplement at minimal cost.