You can’t stop them from moving, but you can conditionally put a coverText on the next slide in the screen CL (by where it says “Teacher Tips” to the left side).
coverText: when yourConditionHere "Go back and try again." otherwise ""
coverButtonLabel: "" #if not here, an "Ok" button let them into the screen
You really want to make sure your conditions are correct. If a student can’t produce the result you want, they’re locked out. So, if the third slide is conditional on the second, which is conditional on the first, you can have students locked out of a lot of an activity.