I'm getting lots of fraction questions lately...must be close to testing time! There are so many important teaching points here. I think this addresses that we can only add like things together. If they aren't alike, we have to find a common term. That's true in first grade. When we add circles and triangles, first we have to find the common term, shapes. In fractions, if our denominators aren't alike, we have to find the common term before we can add them!
How does this address the common core standards? What extension questions are you asking? Can you step back and bit and teach them to persevere?
I've been playing a lot with the open number line lately. It's a great way to add or subtract and works with all grades. Each student can approach it at their level (which makes a great assessment!) I love to have students do it by themselves and explain their thinking. This is a great way to have students see more efficient ways of solving the problem. It's also wonderful for children who have trouble with subtraction...they now see that it's just a relationship between two numbers. The video shows examples of two digit and three digit numbers and numbers with decimals. If your students understand the concept, they can take it to fractions, elapsed time, and measurement!