Problem: My students have such a hard time with unknowns in all positions of math problems. (Common Core standards 1.OA.A.1, 2.OA.A.1)

Solution: Give them plenty of exposure to part-part-whole!  It seems so basic, just a way of showing the two smaller numbers that combine to make a bigger number.  As shown on the picture, 3 and 6 are the parts, put them together and 9 is the whole.  It can be shown with circles (called number bonds or math mountains when turned to point upward), made with cubes, and represented with equations.  Look at how part-part-whole helps with an unknown at the beginning of an equation:

Rachel had some pencils.  Her teacher gave her 6 more pencils.  Then she had 9 pencils.  How many pencils did Rachel have to start?

We know the whole is 9 and one of the parts is 6.  Using a part-part-whole representation kids can find the missing part either by counting on or by subtracting.

Hannah Braun
Hannah Braun is a former teacher with 8 years of experience in the classroom and a master's degree in early childhood education. She designs engaging, organized classroom resources for 1st-3rd grade teachers.