I think the main difference in Curriculum by Programs vs. Curriculum by Years is in how much students of the same family can work together. The former program was my effort to allow families to share in books and topics more frequently (although not always) than the latter scope and sequence. Curriculum by Years follows a year by year approach similar to Ambleside Online, while Curriculum by Programs follows a program by year approach similar in some ways to Charlotte Mason's PNEU programs. The Foundations Guide is a program guide for the early years, including Year One. Since formal lessons are not meant to start until Year One, complete lesson plans will only be written for Year One students for the Foundations Guide. There are sample schedules, but the thought in this guide is to keep lessons lighter and more flexible, particularly for the Pre-Preparatory and Preparatory Levels. Children will move on into Lower School B after Year One is completed or when parents feel their student is ready for it. This level combines Years Two-Four, but Year Four will have less in common with Year Two and Year Three students in that they will still share the same time period of study overall and share some books together, but they will also have more books of their own-books which reflect their growing maturity. The schedules are aligned as much as possible and picture study, music appreciation and many other studies can be shared as well. Program 1 focuses on Pre-17th Century history, so students in this program will study Native Americans and early settlements of America. Students in Year One will also study Native Americans and the story of the first Thanksgiving, so this aligns well with this guide. Year One students always study these topics, since they are not part of the historical time period divisions. Program 2 focuses on 16th-18th Century history, so these students study this time period in American history. A student would begin in Foundations and then move on to Program 1, 2, 3 or 4, depending on where you want to begin you study of history or where your older students are in the study of history. Lower School B is always designed to meet the needs of students in Years Two-Four no matter what time period they study. The idea is that you would then move on to the next program the following year. Curriculum by Programs does not make it so that you would not have to buy a new program or set of lesson plans each year (you would have to do this with the Curriculum by Years plan), but that if you choose this approach with children of varying ages then they can be kept together in at least the same historical time period, picture study, songs, etc. as well as children closer in age sharing many of the same books. For example, your children could start in Foundations and Program 1: Lower School B together. The schedule allows for the flow of the day to be similar and you choose whichever artist, song, composer, handcraft, etc. you wish for both children to study together. A couple of the books used for American History in Foundations will also be read in Program 1: LSB. The following year, your Year Two student will move to Program 2: LSB along with your Year Four student. Both children can work from this Program guide. However, you will need separate lesson plans, since Year Two and Year Three students have one set and Year Four students have another. This is because of the differences in book titles and expectations. The following year, both students will move to Program 2 -with one student still in LSB, but the other now in LSA (Years Five and Six). Again, students will study the same time period and you can choose new composers, artists, etc. so that both students can share this study. Some books from LSB might be shared with students in LSA, but usually only a few. Books chosen for reading aloud during the Children's Hour can be selected to best augment sharing. Older students will also be given books to read independently, so this will help offer appropriate upgraded choices as well. Some years will have students studying the same thing, no matter which program they are using. For example, in Year Three, all students will study their home country and read Paddle-to-the-Sea. The additional book for geography for that year will change according to the time period, but the former books will stay the same. Students who follow the Curriculum by Years guides will each work through each year independently. The schedule does allow for a better flow of joining students together, even with this plan, in that children will take breaks, have nature experiences, sing songs, study foreign languages, etc. at the same time. You could certainly also adapt this approach so that more books are shared, particularly during the Children's Hour. Once you buy your student's complete guide for that year, you can certainly use it again with a younger student. If I make any major changes, I'm usually pretty happy to offer you the new updated version for free. I try really hard not to let my changes overly affect your budget. :) I hope this helps.