The Henle Latin series, originally published in the 1940s, is a four-volume set with books titled First Year through Fourth Year. This is a classical program that begins by teaching the grammar of Latin. Students memorize declensions of nouns, conjugations of verbs, vocabulary, and other elements as they gradually learn to translate, read, and write Latin. Students cover the traditional Latin literature sequence of Caesar, Cicero, and Vergil in Second Year through Fourth Year. There is Christian content throughout the series, and some content is specifically Catholic.
Henle Latin is best for high school, but advanced students might begin First Year in eighth grade. Even with many high school students, you will want to take two years to complete First Year.
Loyola Press publishes the Henle textbooks and answer keys for the textbooks. The grammar forms and syntax rules are all gathered together in a separate reference manual (also published by Loyola Press) called Henle Latin Grammar. This grammar manual is a required reference book for all four Henle textbooks.
Memoria Press has been selling the Henle series for years while also using it in their school and online academy. They have developed teacher resources that make it easier to teach the courses. (New teaching videos are available for the first year, and I expect the videos will eventually cover more years.) Memoria Press also publishes Quizzes & Tests books and Vocabulary Flashcards sets for the first three textbooks, as well as student guides for Second Year and Third Year.
Memoria Press teacher resources vary for each of the first three years, and they do not publish support materials of their own for Fourth Year. Henle Latin: First Year has enough content that you can easily spread it over two years, especially if students begin the course in eighth grade. Consequently, Memoria Press has two teacher manuals for First Year that split the course in half. These two teacher manuals have some instructional information as well as lesson plans. Second Year has only optional lesson plans for the teacher. Only a student guide is required since students can work independently through that course. Third Year has both a teacher manual and a student guide. The teacher resources include check-off boxes for assignments as well as for daily drill and recitation practice. The teacher manuals and student guides coordinate the use of Henle Latin Grammar with the first three textbooks, but the Henle textbooks also provide this information. Only the First Year Memoria Press teacher manuals include answer keys for the textbook. The Loyola Press answers keys are needed for the other courses.
In the First Year textbook, grammar and vocabulary instruction takes precedence as students work through numerous practice exercises. Some are labeled “essential” for students who master the material quickly and need not do all the exercises. Memoria Press has created online instructional videos for this course that are bundled to align with their two teacher manuals. (When you purchase these videos, you get lifetime access.) There is one video for each week's lesson content. Presenter Jon Christianson leads students through recitations, explains new Latin vocabulary and grammar, and discusses some of the assignments and exercises. Parents and teachers should still have students do recitations on other days than when students watch the video.
The Second Year textbook reviews the material taught in First Year. In the Second, Third and Fourth Year textbooks, the first half or more consists of readings to translate. In Second Year, notes and definitions are at the bottom of the pages (footnote style), while Third and Fourth Years feature copious notes, background, and explanations on facing pages. Exercises are found in the second half of each of these three textbooks, with accompanying instruction on new concepts. Reference helps and Latin-English and English-Latin vocabulary lists are at the back of each textbook.
The Third Year: Student Guide helps students work independently through some of the lesson material. Rather than a workbook, the guide gives assignments, word studies, exercises, and explanatory notes. This course focuses on translation work, so a teacher needs to be involved.
The classical approach of this series fits perfectly with other elements of a classical education, but it can also be used by those not pursuing a classical approach for other subjects. Henle Latin is an excellent, traditional Latin course, but you really need the Memoria Press resources to make it practical for homeschooling.