Our school used curriculum based assessment when trying to determine a math placement. At the start of his 2nd grade year they gave him an end of the year assessment of the 3rd grade curriculum. His performance on that made the principal suggest subject accleration to 3rd grade math. For our school the subject acceleration (even whole grade acceleration) as been the best option because the principal doesn't want to demand "too much" of his teachers in terms of differentiation.
As for the letter and number reversals - be sure to provide a letter/number line in view at all times to help your child learn the correct way to write them. Most, not all, just need that visual reminder to turn it around. You can even just provide a visual cue with only the letters/numbers that are reversed if your child is consistent with just a few. If you don't correct them they never get corrected!
