I think STAR testing is pretty close to CASSP testing. DS also took NWEA for many years. The last couple times he took the NWEA ending in 6th grade he has a 99% in both subjects. He had perfect CASSP scores for three years in a row. But he had to study a lot of get high ISEE scores. He is also taking Geometry as an 8th grader. Is first SSAT is a 90. He’ll take it again.
I’d recommend taking a few solid sample tests and get a sense of where you fall. It is pretty normal to repeat a year in bs, in fact it would be my plan for my young daughter.