We have used Horizons from grade K with no problems. My oldest used PreAlegbra this year, and I will not be using it again. The teacher's manual offers almost no help in explanations that go beyond what's already in the student's book. In some lessons, that was a problem. Several of the problems assigned at the end of the year are beyond what should be expected for a 7th grader. The descriptions in some reading problems are so poor that it is difficult to understand the scenario that the author is trying to describe, which makes it impossible to solve the math portion of the problem. Some problems are meant to be given in "every day" scenarios, but then the answers don't make "every day" logical sense for what people who do in real life. IF I used this again, I would skip certain lessons/problems that aren't well thought-out.
Pre-Algebra is just as straightforward, just as easy to use, and just as challenging. I think the problem sets are actually more reasonable than the younger levels. Horizons math is slightly advanced and it requires a lot of hard work. If the student has "grown up on" Horizons, she will be able to do these with no complaint because the foundation has been laid well. We LOVE that the explanations are short and sweet, because she doesn't need any more explanation! I do recommend adding Zacarro's Challenge Math to solidify problem solving skills. We are thrilled with Pre-Algebra, and my dd scores above 90% in all her state tests.
This math curriculum/workbooks don't give me anything to "teach" my child in the parent's book and doesn't really explain much in the student's book. My child is getting frustrated in his math. In public school, he was in advanced math, homeschool, he doesn't understand much. I have to keep going over things with him and/or finding Youtube videos to explain it.
We've used Horizon's Math for five years and it is, by far, the best math curriculum available. I have two girls that can sometimes get pretty frustrated with the more difficult lessons, but with Horizon's that frustration is usually short-lived. It will introduce a difficult activity and then go back to easier tasks that build back up to the more difficult ones. It's bright and colorful pages keep their interest piqued. Since we started Horizon's, my girls stay 2-3 grade levels ahead in math!!
I have used Horizons K-8. It has always been a bit fater paced than the "average" math curriculum in ALL their subjects. I would not recomend this for any student who has not completed Horizons grade 7 or is a strong math student. It moves just as quickly as any other Horizons. I found the classwork to be far tougher than the tests. I appreciated the practical application aspects. It does well in covering the topics and teaching application. There is not a ton of practice on each concept, but more than enough for a GOOD math student that would get bored the extreme repetition. I am more than happy with it. I have bought Grade 8 and can't wait for grade 9.