The most common and most likely answer to this crossword clue is the 5 plus 9 letter word BASIC EDUCATION
B
A
S
I
C
E
D
U
C
A
T
I
O
N
Buddy explains!
The straight part
We know that "the three Rs?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case the three rs? = basic education.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.