I was working on this activity:
Yesterday, it had the “check correctness” button at the top of the student preview, so the students could know when it was correct. Today, it is gone.
Can you please tell me what happened? I want the students to have immediate feedback on their work.
I think you’re thinking of the teacher tool that you see while previewing an activity that you are editing. When students work on the activity, they won’t ever see any feedback unless you build it in for them to see. The default correctness really only shows up for the teacher on the dashboard.
Looking at your activity, I see several places where you have a message appear in a note, for example, when the MC choices are correct. That’s the kind of thing you always need to do when you want them to see correctness.
Thank you. It isn’t really clear that it is only for the teacher to see. 
I was able to write code into the questions, but I thought pressing a single button would be easier. Probably something for Desmos to consider, as this topic is pretty common on the forum.
Maybe not the answer you’re looking for, but it does specify “Dashboard Preview”, meaning the symbol there is what you’ll see on the Teacher Dashboard, while the rest is the “Student Preview”.
Regarding “pressing a single button”, the desired student-visible feedback can be quite variable, and there’s not really a one-size-fits-all solution. Are you saying you’d maybe like an option to have that button available to students? It’s currently only a dashboard button.
Thanks. To answer your question of "Are you saying you’d maybe like an option to have that button available to students? " Yes! That would be awesome! Although some teachers may want to have more control over the student feedback, if there was a way to opt-in to showing some basic feedback (correct, not correct), that would solve most of my CL problems. I’m sure there are others who could use this too. This would just be the “matchesKey” command.
By the way, this is my updated version: https://teacher.desmos.com/activitybuilder/custom/65fc596985c35f6fbd8805be
If I really want students to see if they are correct or not, sometimes I will anonymize the names and project the teacher dashboard for everyone to see. But Desmos is designed for more meaningful feedback than just correct/not correct, so I don’t think they have any plans to make that kind of feedback easier to give.
Wouldn’t it be cool if, when students submitted their angle measure, you had an animation to show how big their answer was in relation to the actual angle? I know it’s a lot more work to figure out though, and sometimes animations make the questions more guessable, and then you have to limit attempts. So if you really need correct/not correct, I would just project the dashboard.
Unfortunately I am not able to do that in my current curriculum schedule, which is why I need the correct/incorrect. I’m using Desmos for them to explore the relationships and build the formulas, then I want them to practice using the formulas they made. If you look through the activity, you’ll see that the first half of the activity is group discussion. The rest is their individual practice - some of which will be done as homework, which means I won’t be with them to tell them if they are right or wrong.
When I’ve searched for CL code for this kind of thing, there are countless people asking for ways to give correct/incorrect feedback to students. It seems like this is a much-needed feature.
