Regardless of the curriculum previously used or the grade earned in a prior math course, the best placement is the textbook designed for their current grade level.
For a good, strong or average math student in 4th grade we recommend:
Saxon 5/4 with DIVE Video Lessons
A Placement Test is not recommended*
*Saxon did not make a placement test for Saxon 5/4. However, Saxon & Shormann Math placement in Kindergarten through Pre-algebra is based primarily on developmental readiness (grade level). The first 30 lessons in each level review the prerequisite concepts needed for success in the course, so placement tests can sometimes place students lower than necessary.
For this reason, only gifted math students who may be ready to advance one level should take a placement test. Students who are reluctant, struggle with math, or have gaps in their understanding are generally more successful starting one grade level lower.