Self-checking activities allow students to have immediate feedback on how they are doing. When these activities are completed in small groups, it gives students an opportunity for meaningful mathematics discussions. Students determine if they have the correct answers and if they don't, they can work together to determine where their mistake is. This allows the teacher to focus on groups that have misconceptions or misunderstandings as students will often find and correct their own computational errors.
A self-checking activity that I've recently been using is called "Odd One Out." I was inspired by a couple of activities that I found on TES. The first example was a page showing a number of expressions to evaluate using the order of operations. In the center of the page was a bank of possible solutions. There were 15 expressions and 16 solutions. The solution left over when all the expressions were evaluated was the "odd one out." The other example showed four sets of five linear equations to solve. All of the equations in each set had the same solution except for one. The goal was to identify the equation with the "odd one out" solution.
Below are two "Odd One Out" problem sets that I created. The first one is to practice solving systems of equations and the second is to practice solving precentage problems.
You could also use this activity as a quick warm-up with fewer numbers. Jo Morgan (@mathsjem) shared an activity from MathsPad on her Math Gems #74 that had a sets of 9 radicals (surds): 4 simplified, 4 unsimplified and 1 odd one out. You could also use the same format as above with fewer questions. A couple of short examples below.
Craig Barton (@mrbartonmaths) highlighted Odd One Out activities in a "Maths Resource of the Week" in late 2016. He describes a few different varieties of this activity and also points to a variety of different examples of this resource.
Have you used an odd one out activity with your students? How did you use it?