I knew the math wasn't too complicated, but I haven't really seen my students do a lot of this type of problem yet as we have been so focused on number lines and place value. I gave them a little time to work and told them to do the "Extra" part if they finished early. What you can't see is that the bottom of the page has the lines for them to explain their work (this is one of the formats in my word problem sets . . . I love them!)
As the students finished, I asked them to share their answers with me and I wrote them on the easel. If students had the same answer, I added a check mark. After they had all finished the first part (note--this was only HALF my class . . . we had 2 groups today!), we talked about strategies for solving and drew the sketch at the bottom of the easel. Students were pretty confident about their answers (the "14" kids were just as confident as the "28" kids!). As we were talking through it, I saw a few kids frantically making changes.
I stopped the group and asked what was going on, and one of the girls said, "Something _____ said made me realize my mistake!" We had a great discussion about the problem itself (not challenging--but one that needed to be read carefully) AND how important it is for mathematicians to think about reasonable answers (19 was NOT reasonable for the extra part!), to listen to the explanations of others, and so on!
We then spent a few minutes sharing out some of our written explanations and noting what we felt made a quality response. We'll try it again tomorrow with another problem and see how it goes!