The History of the ____ World books and Study Guides are recommended for 9-12 grade and adult learners.
For students younger than 9th grade, we recommend that you use The Story of the World. Follow the recommendations in the front of each activity book under "Multilevel Teaching." This will tell you how to make the material more challenging for a middle school student.
The Well-Trained Mind, 4th Edition discusses the ways that grammar (elementary), logic (middle school) and rhetoric (high school) students differ in their development, interests, and capabilities. Elementary students focus on fact acquisition; middle school students focus on the relationships between the facts. An elementary student might memorize the names of the Kings of England or learn about World Wars I and II, the logic student will focus on the impact a particular King of England had on the history of France, or how one World War left unfinished business that caused another. You use the same texts--SOTW--but in different ways. The Well-Trained Mind goes into further detail about appropriate content and methods for each age group.
By the time a student is in 9th grade, it is time to move on to more complex and adult learning: forming opinions, expressing them, and persuading others. This requires richer content, which is provided in HOT_W. The logic student is most likely not ready for the reading level and some of the content in the HOT_W series.
Although the time periods are the same (Ancients, Middle Ages, etc.), the HOT_W books cover much more information and the information is presented in a way that doesn't align the two series. However, extracurricular activities like going to a museum, watching documentaries will coorinate if you place them all in the same time period.