Free Online Homeschool Curriculum
While there are a few websites have all (or almost all) of what you need on their website, many of the websites also use books that are free to download or read online. Some require you to get a book from the library, and then others will have free instruction for a college or high school textbook that you would need to buy. While the latter is not completely free, the instruction is, which I think qualifies as a freebie!
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Ambleside Online  is a free home school curriculum designed to be as close as possible to the curriculum that Charlotte Mason used in her own private and correspondence schools. Ambleside Online recommends the highest quality of books and most of the books could likely be found through a library loan system. The curriculum also uses as many free online books as possible, and there is no cost to use this website or join the support group.
Old Fashioned Education
Old Fashioned Education  offers a directory of free home school curricula, literature and text books organized for the use of home schooling families. It has its roots in Charlotte Mason, but has a more structured routine and schedule. There is a book list, daily schedule, and many other resources for each grade level from K- 12. One of my favorite things about this website is that there is a section where you can find numerous websites to find free online books! Even if you don’t agree with all of the ideals presented, this is a useful website for planning your school year.
PASS (special learning needs)
Complete textbooks in downloadable form (PDF files) for all core subjects are available from the Parallel Alternative Strategies for Students (PASS) . These textbooks are written to help students with various learning needs and are presented in an easy-to-understand format. The PDF’s are currently found in the search results from the ERIC educational database, so you will need to scroll through the various results to find the books that you need.
SAS Curriculum Pathways
For grades K-12, SAS Curriculum Pathways  is available at no cost and used by thousands of educators in all 50 states. SAS Curriculum Pathways provides academic instruction of English, mathematics, social studies, science and Spanish. Social studies materials include an interactive atlas. In math, an interactive tool helps students develop basic algebra skills. Enhancements to the award-winning Writing Reviser in the English module help students master sentence fundamentals. Spanish materials help students develop reading and listening skills in real-world situations.
Massachusetts Institute of Technology , also known as MIT, is a private university that has numerous courses available for free online (not for MIT credit, though). What they have is called Highlights for High School and it is your guide to MIT courses selected specifically to help high school students prepare for AP exams so students can also get a glimpse of what they will study in college.
HippoCampus.org  offers Algebra, American Government, Biology, Calculus, Environmental Science, Physics, Psychology, World Religions, and US History. You can follow a course of the curriculum in each class, or select a problem area to get a clear explanation and practice problems. Many of the subject home pages include a corresponding moderated blog created by teachers, for teachers. Each blog contains ideas and activities that teachers can use to use HippoCampus in creative ways. Posted lesson plans include learning objectives, assessment ideas, assignment details, instructor notes, and a rubric for grading lessons. The lessons also utilize some videos from Khan Academy.
Khan Academy  is a not-for-profit organization with a mission to provide a free, world-class education to anyone, anywhere. With over 2600 videos, they cover K-12 math, science topics such as biology, chemistry, and physics, and even reach into other subject with playlists on finance and history. Each video is approximately 10 minutes long, and learning is self-paced. Parents, as teachers, can see any student in detail, have a real-time class report for all students, and see resources for providing targeted interventions in learning if necessary.
CK-12  is a non-profit organization that has a ton of great educational resources! Once you create an account, you will have access to full lesson plans (including several with videos) for math, science, engineering, history, english, and technology! Once you click on a subject, you can pick a specific topic that you want to study about OR you can click on the “Concept Map” option to see the order that they recommend teaching the concepts in. Please keep in mind that this is a completely secular curriculum, so any science lessons that talk about the origin of life would come at it from an evolutionary perspective. If you like utilizing a Kindle, or your Kindle App on your smartphone or tablet, then you can also download A TON of CK-12 textbooks for FREE !
Brightly Beaming Resources
Brightly Beaming Resources  is a full and totally free curriculum for preschool age up to age 11. Brightly Beaming Resources is home to a very popular preschool curriculum called Letter of the Week. Letter of the week works exactly how it sounds… you learn one letter per week with your preschooler and Brightly Beaming Resources gives you the lessons, activities, and book lists.