Q: I have been working with a child for a year and a half and R has been very resistant to improvement. I just stumbled upon a good R in STRI-words like “strike”, “stripe”. Yet he has problems doing what you call “lerring” [sliding back-and-forth between L and R]. Why do you think this is?

R can be a grand mystery and you never know what pattern will cause it to sound right. Just go with whatever works. It could be that he can do a Back R but not a Retroflex R, thus “Lerring” won’t work for him; it depends on which R he ultimately uses.