Say It Right is beginning 2013 year with early detection/intervention month!  Research has shown that the earlier intervention begins, the shorter intervention time is required to master goals
(Jacoby, et al, 2002).  Speech-language  intervention initiated at a younger age necessitates fewer treatment units than if initiated in later years.
For SLP’s working with vocalic /r/,  you will be glad to know that there is also research supporting that 75% of children aged 3 can correctly produce /r/.  (Porter, J.H. & Hodson, B.W. (2001)

Taking the research into account demonstrates that  intervention can begin as early as 3-4 years old if student is stimulable for /r/.  Once correctly produced /r/ word that is all you need to get started.   The Entire World of R single word screening with stimulus cards containing pictures is an excellent way to assess student readiness for /r/ intervention.   Starting /r/ intervention earlier will allow more treatment time  indicate that the outcomes children achieve vary with the amount of treatment they receive.  More treatment time is associated not only with more progress, but also in an  increased proportion of children demonstrating functional  gains in their speech and language skills.

Early developing sounds and flip books are great practice tools for parents to use at home.
Our early developing sounds artculation apps with Mayer Johnson  and Say It Right Early Developing Sounds Instructional book are excellent tools for production and phonological practice.