They do not! Essentials was created for older learners and may be completed without going through Foundations first.
Essentials is a great next step if students who have completed Foundations want to go deeper with spelling, grammar, and vocabulary using the same tools that Foundations introduced, but Foundations is not a prerequisite for Essentials.
Essentials and Foundations are designed to meet the needs of different ages, and a student old enough to start Essentials does not need to complete Foundations first — even if he or she is a struggling reader. All the phonograms and spelling rules taught in Foundations are also taught in Essentials (as well as others Foundations doesn't cover).
However, for students who have completed Foundations, Essentials is a great way to go deeper, learn new spelling, grammar, and vocabulary concepts, and apply what they learned with an emphasis on spelling mastery and more advanced spelling words.
For students new to Logic of English
Foundations is never a prerequisite; Essentials starts at the beginning and builds very systematically, guiding students to become strong readers and spellers as they learn, apply, practice, and master all the phonograms and spelling rules. It is an excellent way for students age nine to adult, as well as some eight-year-olds, to learn the structure of written English and strengthen their ability to read and spell proficiently. Strong readers will deepen their understanding of why the words they can read are spelled the way they are, gain tools for reading and spelling advanced vocabulary, and build spelling mastery. Struggling readers will learn powerful tools and foundational skills that equip them to become strong readers and spellers. And all students will practice these skills while learning grammar and morphology concepts that further strengthen comprehension and composition skills.
Most students under age seven or eight will be happier starting in Foundations, while most older students prefer the style and pacing of Essentials lessons and will be best served by starting with Essentials.
For students who have completed Foundations
While Foundations is not required before Essentials, for students who have completed the Foundations program Essentials can be an excellent next step when they are ready to go deeper with spelling!
In Essentials students will review the phonograms, spelling rules, and linguistic concepts they have learned, but they will begin to focus much more on spelling mastery in the application of these tools. They will also learn the remaining spelling rules, new morphology and language tools that further strengthen vocabulary and comprehension, and many grammar concepts not introduced in Foundations. In other words, they both deepen their mastery of what they have already learned and continue to build new understanding of English that builds on their established foundation.
In Essentials, three levels of spelling lists, grammar practice, and vocabulary instruction in each lesson make it easy to customize the level of difficulty for the individual student. This is one reason that Essentials works well for students who already completed Foundations, because you can choose the level of spelling list you will use based on your student's current level of spelling mastery.
For more information on the similarities and differences between the two programs, see What's the difference between Foundations and Essentials? for a detailed comparison chart, and Do We Want Essentials or Foundations? to help feel out what might be a better fit for a particular 7- or 8-year-old student or a second grade class.