I have used the "Key to..." series with each of my six children and each of them is excellent. The Key to Algebra series is no exception, introducing algebra and its complexities in a very simplified and easy-to-understand format. While I wouldn't use Key to Algebra as a stand-alone course for college-bound students, it is a great supplement and an EXCELLENT starter for those students who struggle with math.
I recently bought the Key to Algebra and Key to Geometry series for my 9and 11yr old home-schooling children. We use the books for self-directed maths sessions for about one hr each per week, in addition to their 'taught' general maths syllabus.I am completely dazzled by these books, they begin at the beginning and very methodically and gently take the child through a very detailed, comprehensive and indeed joyful course. With the odd exception, the child is able to totally self direct. I am surprised by how much is covered in these series and how quickly the child moves on, while still feeling they are 'having fun'! My 9yr old often works on the geometry series in his free time and is now able to discuss with correct terminology, bisecting angles, congruence etc; and I stress this is all self taught. Would say that on completion of these series - which may take us a couple of years - a child would be able to complete the geometry and algebra elements of the UK GCSE public examination - aimed at 16yr olds. I cannot recommend highly enough; I've found nothing like this anywhere else and order from the US - in fact I have ordered other 'Key to' series: metric measurement, decimals, percentages and fractions. The real key to success in maths it is to lay a solid foundation without fear; these books do this and much more.
My 15 year old son is using this product and although he doesn't enjoy Algebra, he is able to understand and do these lessons mostly on his own. I am thrilled with Key to Algebra and do recommend. We like having consumable pages, small workbooks instead of textbooks, and directions are written so that the student can understand and work independently.