Hi Heather-
I don’t know the answer, but I have the same question! My dd- 11years old outgrew transposing by about 6-7 years, but my son who will be 9 in September still transposes numbers and letters frequently. He is a reluctant learner- all boy. I keep hoping he will outgrow this transposing.
He gets 3’s, and 6’s backwards, but will transpose other things as well. We use a trick for b and d. For d we say that c comes right before d in the alphabet, so make a c first then add the stick, and for b I have drawn a bouncing ball that forms the b. I am not sure when he will need further evaluation.
My son is about half way through our reading curriculum, and making progress.
Can your son read?
Do you have access to a child development center associated with a university?