The guides themselves from year to year have built in reviews, as the skills build on one another each year, and as layers of history are added and previous layers are revisited. History is a huge body of information, with too many famous people and events to even begin to count, and as such, it is impossible to memorize completely. Science is the same. My oldest ds has just completed Missions to Modern Marvels, and he has done HOD from LHTH to MTMM through the years. He is now like a walking encyclopedia - or I guess I should say, a 'walking LIVING book' because what he remembers isn't dry and lifeless but rather interesting and full of life.
I have noticed he can join in and talk fairly accurately about just about anything important in history/science, and even in other areas like classical music, art, and poetry. For example, when watching the history channel, he pipes up with this or that to add to what we're watching, or when someone brings up a famous scientist in a speech or in a book, he often adds this or that to the conversation, or when someone mentions a famous line from poetry he can discuss the poet and his style/life. This is from years of reading living books and classical poetry in HOD and completing every single one of the follow-up assignments in each box. I see the beginnings of this with Riley, my middle ds who is doing CTC now.
I am sharing this to show that simply doing the guides in their complete form as written year after year builds an incredible knowledge base. If you were to pluck out one question and expect one certain answer in one certain past studied subject area - true, you may not get an exact answer from dc. BUT, what you will get is a deeper understanding of the subject matter - a familiarity with the famous person, a feeling about what it was like to live during that time, an association of that event with other events that were happening at that same time and how that effected that one happening, an association of that person with another person that was living at that time, possibly a quote or a line or two from a speech that was significant during that time, a description of a poster/book cover/flyer etc. that is famous for that time, and so much more. You get the whole enchilada rather than one single fact, and it is so much deeper.
BUT, you won't get this right away - it takes time and a consistent diet of HOD guides from year to year.
When you think about it, the most meaningful things we ourselves have learned from school that we remember are not individual facts, but rather themes or fuller ideas. For example, I could not tell you a specific name/date associated with famous educators I learned about in my master's program, but I can tell you about different ways to teach using various famous methods and how those varying methods work with different kinds of learners. I don't remember who coined the individual "learning styles," but I can tell you the different learning styles and how to incorporate them into learning. Anyway, I would encourage you to rest assured your dc are learning so much with HOD, and that as long as they are fully doing all that is planned in a guide, they are getting 'enough' and will remember so much more than isolated information. It really is an incredible way to learn and to teach. I hope something here helps!
In Christ,
Julie