I am a busy homeschool mom. I don't have the space to know everything at the drop of a hat. My child uses the DVD (the older edition with Nance) and works on her own. However, I need to help her in her mistakes and misunderstandings on Exercises and Quizzes/Tests. Logic is not as easy to drop in as say, my youngest's 1st grade math page. The TG gives a readable guide to how to teach the lesson (if not using the DVD). It has bold font with the most definitional/important information so I can quickly teach myself also. The teacher guide gives all the answers EXCEPT for the Review questions, they assume you know it or can find the answers in the text. There are just answers to the Exercise, Quiz, Tests, not a full explanation of how they got the answer. So again, I still need to get familiar with the material to assess anything that my child does that doesn't match up to the answer. I wouldn't be able to help my child, or assess my child successfully or efficiently without it. It is worth the investment in my opinion. I am not a TG collector by any means, but some TG are essential. It is written geared toward a group, but is easily (not all curriculum is like this) amendable to an individual student.