Putting on the Squeeze. Teaching Guess and Check as a Last Resort

In a perfect math classroom, no student would ever have to use the guess and check method but let’s be honest…it’s not a perfect world. Guess and check is the fallback method of most students who can’t figure out a problem.
                       
When teaching guess and check it is important to stress that it is a very last resort as it can be extremely time consuming. Here is how to give a bit of direction to reduce the time restrictive nature of the guess and check method.

When my students come up against a question they need to use guess and check to solve, here are the steps I have them follow. 

1. Choose a number that you think is a little bit too high to be the answer. Try that number and see if it works. Was it actually to high? 
2. a) If so, choose a number that you think is a little bit to low.                                                                                                                                            b) If not, choose a number that is higher.
3. Try the second number and see if it works. Is it too high or too low? 
4. By now you should have a number that you know is too high and a number that you know is too low. Which is closer, the high or the low?
5. Choose a number that is between your high and low estimates but closer to whichever one produced a closer result. 
6. Repeat the question with your new estimate. If you’re high, choose something lower. If you were low, choose something higher, but always within your bound. 

Tips for success:

• Start with whole numbers to find an upper and lower bound. 
• If you are stuck between two whole number, eg 3 and 4, then go to tenths, when you get stuck between tenths, eg 3.2 and 3.3, then move onto the hundredths and so on until you reach an exact solution, or one that is really close. 

Though guess and check is not the most efficient nor mathematically beautiful way to solve a problem it is important to teach our students how to use it as a fallback method. One added bonus of having students use the guess and check method is that it gets students to practice estimation skills. 


See how this works in your classroom and let me know if you have any additions that you found. Teaching is best when people are sharing their ideas, successes and failures.