I talk a LOT about teaching using the concrete-->representational-->abstract sequence of instruction. Since I'm often involved in remediation, I see the results of kiddos who are rushed to the abstract stage too quickly, so that is a big focus of mine. I think the best way to illustrate what's meant by CRA is with an example. First grade has been working on addition with 3 addends, and this is an activity I developed for them. First, students use teddy bear counters (concrete). Next, they use ten-frames (representational). Finally, they use number cubes with the digits (abstract), not dice with pips.
Click here to grab your copy.