There is no scope and sequence or benchmarks that homeschoolers must achieve the way public schoolers must. But, I believe it is often helpful to understand what a first grader should know, what a second grader should know, etc. It can be helpful to look at if life circumstances compel us to prepare them to enter formal schooling. It can also be helpful if they are on track to go to college or plan to go to a public or private high school. But, where can you find benchmarks or a scope and sequence?
World Book has a general one that I like for grade K-12. You can find it here: http://www.worldbook.com/typical-course-of-study
I did find a link to the National Core Standards here:
If you look at these, I think they can seem a bit daunting, but if you are trying to develop your own curriculum, they may be very important to understand. All states have standards for education--goals for what skills children are to learn and achieve competency in. There has been a movement among educators to develop one set of national standards. That is what these national core standards are.
On Bright Hub Education, I found that there is a set of curriculum guidelines for several grades.
Here is the first set for first grade. for third grade. for fifth grade... I also liked this list they included for high school.
Lastly, I found this one that I actually think might be really helpful. It also covers what children should/could/can learn about God at various grades. I think this can be helpful because it is often difficult for very young children to understand certain concepts about faith. Also, it can be a list of helpful reminders of what we need to intentionally teach our children about concepts we assume they will learn about in church or that we might assume they already understand. The scope and sequence also does cover all of the core subjects that students learn.
I do look at these once in a while. But, this is one reason I choose a math textbook over writing my own math curriculum for my kids. I want to make sure everything is covered. But, as I plan my US History curriculum for next year (and am putting it together on my own), I will be looking over these sites to make sure I cover the essentials. These sites will help me by giving me a basic outline of what we need to study.
I use the World Book Scope and Sequence for Preschool to help me remember all the basic concepts I need to teach my children. Every 6 months I read through the list and check off what they've learned. So, those are some of the ways I have used lists like these and continue to!