I often explain to students that if they misproduce prevocalic /r/ and substitute

/w/ for /r/ as in west for rest that there can be confusion with  listeners.  I use the EWR 8 deck set

prevocalic  and medial/final /rl/ deck to visually show the difference between

rest as in your bed and west the direction.

 

I place the two cards side by side and visually show them the difference while working on auditory discrimination.


Howay for Wodney Wat is also a great book to use with students for showing definition confusion.