Guidance doc on transitioning from 2-5 to 6+: fall score of 231+ and exposure to 6th grade standards. The recommendation is that a fall score of 231+ should lead to instruction in 6th grade standards and transition to the 6+ test for future tests. The document reports an ~10 point drop from spring 2-5 to fall 6+ testing for the highest performers (>90th %ile), which would suggest that the 2-5 would still be the appropriate test for him in the fall, but that the 6+ would be the correct test for subsequent measurements.
https://www.nwea.org/content/upload...ath-6-plus-Transition-Guidance-MAY15.pdfIf you look at page 5, there is a comparison of common core strands assessed on the respective tests, which, you'll note, includes notable differences.
