Class goes much better when students have the ability to check their own work against their peers'. To prevent the case where the whole class ends up confused because everyone makes the same mistake, this works best if the students have access to the solutions. Here is how this played out in a recent calculus class.
There are two main techniques to evaluate definite integrals: by hand using the Fundamental Theorem of Calculus and numerically using the MATH 9 function on a graphing calculator. I gave the worksheet below to one half of the room (printed on pink paper). I gave the same worksheet with the instructions reversed to the other half of the room (printed on green paper). The effect of this switch was that the problems one half was doing by hand the other half was doing on their calculators and vice versa. After students completed the worksheets, I had them find a friend with a different colored sheet. Since the manual and calculator methods for finding integrals are so different, students were unlikely to both make the same mistake. I didn't have have to provide the solutions, the students generated them themselves.
I started this blog to share my transformation from math nerd to math nerd who loves to share math with young people. I teach high school in Philadelphia, Pennsylvania. Your comments are always welcome.