Saxon has placement tests available. We have links in the course descriptions, but no need to go hunting for them. We have them right here as well.
Go to http://homeschoolwithsaxon.com/PlacementTests/middle_placement.pdf to get to their middle grades placement test.
The Algebra 1 placement test is at http://homeschoolwithsaxon.com/PlacementTests/hs_a1_placement.pdf
The Algebra 2 Placement test is at http://homeschoolwithsaxon.com/PlacementTests/hs_a2_placement.pdf.
Go to http://homeschoolwithsaxon.com/PlacementTests/middle_placement.pdf to get to their middle grades placement test.
The Algebra 1 placement test is at http://homeschoolwithsaxon.com/PlacementTests/hs_a1_placement.pdf
The Algebra 2 Placement test is at http://homeschoolwithsaxon.com/PlacementTests/hs_a2_placement.pdf.