How would you answer this 1st grade test question. Explain your reasoning.

[Codeine]

100. He probably did that twice.

Once the "ten-box/tens-block" system is laid out it becomes as instinctive and immediate as any other simple mental math, but because it uses the simplicity of tens it seems to lead to right answers more often.

The best part is that a child with facility for math can immediately move past the physical tens-box stuff and do the two-step operation in her head while a kid who learns more slowly can stick with the boxes for a few more lessons, and each time she does it she's further reinforcing the mental-math concepts at the core of the lesson.

Honestly, it looks stupid but it seems to work. Common Core (our kids' school has an even more demanding curriculum called Core Knowledge that goes even further) is making some pretty surprising demands of youngsters but the underlying lessons seem to be giving them the tools they need to rise to the challenge.