RekenMathLine = Rekenrek + MathLine
RekenMathLine is 2 tools in 1. All rekenrek applications are on one side, now you can do a lot more just by flipping it over. MathLine side provides explicit connection between object and number which allows students to quickly establish a constructivist framework - develop concept of number. By giving the option of number correspondence on one side, students can do much more math including operations through a 4th grade math skill level.
Comparing MathLine and Rekenrek: Academic attributes of each side
1- Building concepts are based on 1-to-1 correspondence.
2- This correspondence allows learners to establish a constructivist framework to understand numeracy and math.
3- Provides explicit connection to develop comprehension in number, fluency and concepts. 
4- Especially effective for modeling operations to comprehend procedure. 
1- Building math concepts multiple ways and allows for exploration.
2- Learn through establishing trust in 5 and 10 then subitizing using part-part-whole reasoning.
3- Students then learn the grouping and subitizing of numbers into operations. 
4- Especially effective for conceptual development.
Explicit Connection and Constant Symbolic Connection
The mistake-free 1-to-1 correspondence that provides constant symbolic connection is key to MathLine's effectiveness. By being able to SEE the number corresponding to the groups, learners develop deeper comprehension.
Key To Successfully Using: 2 Tools in One means different ways to use each side
Learners do not use the MathLine side the same way as the rekenrek side. On MathLine, there is a mistake-free connection between object and number. The number you see to the right of the ring always corresponds to the number of objects. The key to MathLine is the 1 to 1 correspondence. It is also important to understand that you do not count on one bar until you have completed the row above.Once you have completed the grouping or counting on bar above, then move to next bar to continue group, counting, or activity.
Align RekenMathLine to Curriculum - Scope & Sequence of support books
Download the Curriculum Alignment Overview doc to see how Focus Series will enrich a curriculum for each:
Building Number and Understanding Operations
Kindergarten  on RekenMathLine
1st / 2nd Grade on RekenMathLine100
3rd /4th Grade on RekenMathLine5x20     
When to use MathLine side or rekenrek side for different math concepts
This list provides recommendation for which side to use for certain math concepts. While teachers have differing opinion, this is a based off of general consensus of teachers using RekenMathLine throughout the United States.