BTW, we did use Harold Jacobs' Geometry course. To my knowledge, Mr. Foerster has not written a geometry course and we found Mr. Jacobs' course to be a perfect fit between the two Foerster courses. I hope our experience may be helpful to others. I would like to diagram and could probably instruct him just from a grammar reference book like the Rod and Staff grammar reference. It requires minimal effort and produces maximum results.
Children learn all of the English prepositions so they can recognize prepositional phrases.
Easy Grammar is easy to teach, to understand, and to correct, but should not be used with younger children who have difficulty with workbooks. My son and I find this program very easy to understand. I hope you find what you need. I used Easy Grammar for one or two years awhile back. But I do think we will be changing to another Math program once my girls get into the Logic and Rhetoric stages.