No prerequisite knowledge of algebra is required. The Key to Geometry series of eight booklets provides a basic introduction to geometry. It is not equivalent to a typical high school geometry course. It might be used as a substitute for a non-college bound student or as an introductory course for a student who needs to mature before getting into geometry. One booklet looks manageable to a student who might be overwhelmed by a two-inch-thick hardback text. However, multiply this booklet eight times and there is still a decent amount of learning taking place.
Construction with compass and straight edge, combined with inductive reasoning, are the primary learning tools. Proofs and theorems are lacking, but students can build a beginning foundation without them. The publisher is very conscientious about stating clearly that this is not a full geometry course, but schools are using them with students who need a simpler course. So homeschoolers should be able to do the same. Just be cautious about misrepresenting it as a college prep course. (List it as Introductory Geometry on the transcript.)
The books have large print, so students go through these very quickly (ten pages a day is reasonable). They are largely self-instructional. Books One through Six have only 55 pages each, while Book Seven has 154 pages and Book Eight has 138. The entire course should take about twelve weeks, so you will need to do something else for the rest of the year. Also, consider using this course as a geometry supplement for Saxon's Algebra 1 and 2.