An example of Khan Academy Bad Design. Here the activity asks students to read Adsorption Lines, using the traditional “Five Right in a Row” formulation. But in this case five right in a row will just lead to frustration.
Why? Because for this particular concept even being able to do it once indicates a grasp of the concept. At the same time there are certain quirks to reading these lines (just getting the scales lined up) that mean that you will occasionally fail even though you get the concept. This is frustrating for students at best and at worst it can suggest to competent students that their correct understanding is wrong.
The solution here is to key the number of correct “in-a-row” answers to the concept we are attempting to transfer.
Source: Bad Adsorption Activity