Hi, I created an account just to add my two pennies :) We used Teaching Textbooks Level 5 for my 4th grader this year. For background, this has been our first full year homeschooling (K-3 in public school), math is one of dd9's favorite subjects, and she is a quick learner. Neither of us minded TT, but we are switching to Horizons 5 next year. One thing I found is that the beginning lessons of Horizons 5 pretty much pick up right where TT5 left off. I know I've seen here on the forums that children have fared just fine on standardized tests after using TT5, even without bumping up a level. I could be wrong, but I can only assume this just means that Horizons (among other math programs) is that much more advanced, as opposed to TT being far behind. HTH!