There are two significantly different versions of Essentials.
These books are not compatible with newer Essentials Teacher's Guides and Workbooks.
The 2nd Edition (published in 2015 and 2018) and all subsequent editions have 30 multi-level lessons. In this updated and expanded version of Essentials, each lesson, or unit, contains three levels of application: A, B, and C. The newer editions divide the lessons between multiple Teacher's Guides and Workbooks to keep the books a manageable size.
All books from the 2nd Edition and later are compatible with each other. They are not compatible with the 1st Edition books.
The reason newer editions cannot be used with 1st Edition books is that the 2nd Edition was an extensive rewrite and expansion, with lots of new content and updates.
All Essentials books starting with the 2nd Edition (2015) are compatible with each other. The content of the lessons is the same. There have been only minor corrections and clarifications, and changes in how the lessons are packaged, since then.
The Essentials 1-7 and 8-15 Teacher's Guides (2018) contain the same fifteen lessons as the Essentials Volume 1 Teacher's Guide (2015), and the 1-7 and 8-15 Workbooks may be used with either version.
The Details: Changes and Compatibility
Essentials 2nd edition, released in 2015 (Lessons 1-15) and 2018 (Lessons 16-30), was a major revision and expansion of the Essentials program, including two additional levels of spelling lists, grammar practice, and vocabulary instruction in each lesson besides the beginner level in the 1st Edition.
With this update, Essentials now includes additional grammar concepts, advanced phonograms, and morphemes that were not covered in the original (2012) edition. The most significant change in the new expanded version, though, was the three levels of spelling lists, with corresponding multi-level practice activities and vocabulary instruction, in each lesson. The new vocabulary sections introduce over a hundred new Greek and Latin roots.
To give you a sense of the scope of the expansion: the 1st Edition Teacher's Guide had all of Essentials in one book with 612 pages, while the new Teacher's Guides, which divide the lessons into multiple books, have 1,460 pages between them!
The first fifteen lessons of the expanded new edition were originally released as Essentials 2nd Edition, Volume 1. This corresponds to the first half of the original edition of Essentials.
In 2018 we made a formatting change: we began selling these same 15 lessons in smaller sets of lessons: Essentials Lessons 1-7 and Lessons 8-15. We also released the second half, Lessons 16-22 and Lessons 23-30. Each lesson includes three levels of application and practice, so students can complete all thirty lessons at one level, and then repeat an additional time for deeper mastery by starting back at Lesson 1 using the next level up.
Some of the books, such as the 1-7 and 8-15 Teacher's Guides are now in 3rd or later editions, but this is a minor change and does not affect compatibility. They contain the same lessons and are fully compatible with all materials from the 2nd Edition.
To learn more about specific changes in different editions of Essentials books and other LOE products, visit the Product and Edition Details section of our Help Center.