Last month, while an associate sub, I walked out of a middle school math class thinking, "Wow! That was fun!" The students spent the first part of the period using the Percent Of activity on this website - http://www.mathsisfun.com/numbers/estimation-game.php - to hone their estimation skills and increase their number sense. Some of those with higher scores explained their thought processes to others. They all enjoyed trying to improve their outcomes, and most succeeded.
Previously, the class had worked to determine which of three restaurant patrons was the most generous tipper, so the next activity expanded on that. The teacher projected a chart with several dollar amounts across the top and percentages (1%, 5%, 10%, 15%, 20%) down the side. Students worked in pairs to complete the chart. Listening to their conversations was great fun. Most pairs were diligently calculating each result, but I started to hear a few talk about the relationships between the percentages. The most exciting moment for me was when one boy looked up at me with a grin and exclaimed, "There's a pattern to it, isn't there?"
I applaud the teacher for this example of math being taught and learned the way it was meant to be - with a combination of cooperation, collaboration, communication, creativity, and critical thinking.