Why Some Tools Work and Others Don't

I recently saw this math suggestion at another site, and my first reaction was, "COOL!". But then I realized this particular activity wasn't going to be worthwhile for my kids. Why?

First off, it has everything going for it. It has a seasonal touch. It emphasizes fine motor skills, plus one-to-one correspondence and counting. So what's wrong with it?

It has no verification. A child could put four buttons on that 7 snowman. And unless I'm able to catch his mistake, the child would learn nothing from doing this concept builder. And he would go happily on his way putting the wrong number of buttons on each snowman until he either tired of the game, or I rang the bell signaling an end to the session.

But there is a way to fix this!
1. Have the child work with a partner, preferably paired with an opposite. (Ex: strong with weak) That way the student with the stronger math skills can help correct errors as soon as they're made.

2. Have a fixed number of buttons. If there are, say, 5 snowmen to work with, and each snowman has a specified number of buttons to place on it, have that exact amount of total buttons in the bag. So if the child has to put 6 buttons on the last snowman, but there's only 3 left to use, he knows he miscounted somewhere and has to go back to find out where.

I'm very careful about using "open-ended" activities that don't provide a way to check/correct errors. If the students are supposed to get some good out of these cute centers, then there has to be some accountability to them.