At this stage of learning, making ten is a great strategy for a problem like 8 + 5. But the strategy doesn't help you in a problem like 12 + 3. To solve that problem, at this stage of learning, I'd say you want to
- appreciate the place value structure as 10 + 2 + 3,
- know from memory that 2 + 3 = 5, and also
- understand the meaning of teen numbers so that 10 + 5 = 15.
And in general, each region of the a + b map has its own story. This graphic shows the map with different regions color-coded.
Here is a key to the colors:
I use this map to orient myself toward my kids' learning as they progress toward fluency with addition facts and knowing them from memory. For example, the image below shows the worksheet I made for today's Saturday School. (Downloadable PDF here.) You'll see that the worksheet has 36 sums for practice—precisely the 36 sums that are coded yellow above. This is an intense practice day for making ten. Over the past few Saturdays, we established that the partners of 10 (magenta) were down cold, that there was fluency within 10 (red), and that the structure of the teen numbers was well understood (green). These are the key prerequisites for making ten. (Another is the ability to use properties of addition where helpful.)