The eleven units in the book focus on the grammatical areas with which Len's advanced ESL students at Brooklyn College have had the most difficulty. Each unit includes a simple statement of rules related to a particular grammatical area, followed by examples of correct use, and exercises. At the end of each unit, there are proofreading exercises -- with sentences, paragraphs, and essays written by Len's ESL students -- which include errors related to the previously presented grammatical rules. In the final proofreading exercise, Len indicates in the left margin the type of mistake that students should look for and try to correct on each line. This is how Len marks grammatical errors in his students' essays, except that he also underlines the errors to be corrected. So the exercises in this book are more difficult, since students must first find and then correct the indicated error. In later exercises (in units 8 to 11), Len indicates the types and number of errors at the end of each paragraph rather than on each line. In a few units, Len gives "Grammar Observation Exercises," which simply give examples of correct use of the grammar area being discussed (which do not need to be corrected). At the end of the book is an Answer Key that students can use to see if they have done the proofreading exercises correctly.