There is a strong tendency among home school parents to think that a student must complete one mathematics book each year. Sometimes teachers will not want to switch to half lessons, or assign supplemental practice, for fear the student will "fall behind."
No! That is the wrong way to think!
Firstly, the student is beginning in Saxon 3. From the beginning, this places the student two to three years ahead of the average school student. Stop worrying.
Secondly, the goal of education is not to complete a book, or "keep up." The goal is for the student to learn and know mathematics, and the thought patterns that come with mathematics. This is done by challenging the student. What is challenging for one student may not be challenging for another student.
Mathematics education is not a race. Allow other people's children to progress faster than yours. That is not a problem. Some siblings will do better at mathematics than others. That is fine. There is a statistical tendency for boys to do better at advanced mathematics than girls. Don't damage your girls by forcing them to keep up with a brother.
A huge advantage of home school is that each child receives an individualized education to maximize potential. Don't force your children into a mold. This is one of the reasons public school students who are doing poorly usually do so much better in home school - they are free from the restrictions of a classroom or government mold, and receive individualized instruction.
When the student completes Saxon 3, the student begins Saxon 54 on the following day. Begin with whole lessons daily. If the child becomes bogged down and spends excessive time on math, switch to half lessons as described below.
Home school mathematics education is not a race. The education must be altered for the needs of each individual student.