What do you use? My RAs suck. I need them to complete a 100+ hour course to get them up to par.
Resources to train RAs in R for efficient data reading/cleaning/basic analysis

Datacamp is s**t. Follow these:
R for Datascience by Hadley Wickham: https://r4ds.had.co.nz/
This will teach all the basic stuff(and some advanced stuff) enough to do your RA job.If your RAs are a bit more interested in learning then Introduction to statistical learning : http://wwwbcf.usc.edu/~gareth/ISL/
This has all the codes for all the chapters, so great for learning simulations, basic statistical techniques, and Machine Learning.To learn good graphics in R: R graphics cookbook: http://www.cookbookr.com/Graphs/
Finally to be a solid professional:
Advanced R: http://advr.had.co.nz/
Advanced ML: https://topepo.github.io/caret/index.html 
Datacamp is s**t. Follow these:
R for Datascience by Hadley Wickham: https://r4ds.had.co.nz/
This will teach all the basic stuff(and some advanced stuff) enough to do your RA job.
If your RAs are a bit more interested in learning then Introduction to statistical learning : http://wwwbcf.usc.edu/~gareth/ISL/
This has all the codes for all the chapters, so great for learning simulations, basic statistical techniques, and Machine Learning.
To learn good graphics in R: R graphics cookbook: http://www.cookbookr.com/Graphs/
Finally to be a solid professional:
Advanced R: http://advr.had.co.nz/
Advanced ML: https://topepo.github.io/caret/index.htmlFor once someone followed up their criticism with some valuable information on EJMR.

Datacamp is s**t. Follow these:
R for Datascience by Hadley Wickham: https://r4ds.had.co.nz/
This will teach all the basic stuff(and some advanced stuff) enough to do your RA job.
If your RAs are a bit more interested in learning then Introduction to statistical learning : http://wwwbcf.usc.edu/~gareth/ISL/
This has all the codes for all the chapters, so great for learning simulations, basic statistical techniques, and Machine Learning.
To learn good graphics in R: R graphics cookbook: http://www.cookbookr.com/Graphs/
Finally to be a solid professional:
Advanced R: http://advr.had.co.nz/
Advanced ML: https://topepo.github.io/caret/index.htmlAlso I forgot our one and true savior: StackOverflow

Had an RA that didn't even know ctrlc ctrlv. R would be seriously way too advanced.
Bank of Canada broIt's not that R was way too advanced. Without any notion of how to right down a simple algorithm to solve a simple problem, any programming language is too advanced.
Once one can write down the steps to code in some informal pseudocode, then it's nothing to convert that into an R program. Don't know how to write proper syntax for a "for" or "while" loop, google it. Want to find out how read a column from a data frame, google it.
One has to spend an hour or so showing inexperienced people how to get work done with an unfamiliar programming language. That's all. The rest is up to the person to stick with it.