Bookworms have 6 grades and more than 30 books. I remember it started with 800 words and ended with 3000 words. I personally finished watching Lv5 and Lv6. Frankly speaking, it's of little use. For people with good English skills, 3,000 words is only the basis for graduating from high school. The bookworm's audio book is pure English, with a gentle and unpretentious tone, which is suitable for repeated listening practice.