Concrete Representational Abstract (CRA) is a three step instructional approach that has been found to be highly effective in teaching math concepts.  The first step is called the concrete stage.  It is known as the “doing” stage and involves physically manipulating objects to solve a math problem.  The representational (semi-concrete) stage is the next step.  It is known as the “seeing” stage and involves using images to represent objects to solve a math problem.  The final step in this approach is called the abstract stage.  It is known as the “symbolic” stage and involves using only numbers and symbols to solve a math problem.  CRA is a gradual systematic approach.  Each stage builds on to the previous stage and therefore must be taught in sequence. (Research-Based Education Strategies and Methods “Making Education Fun” website)