Go through the lab(like you were a student and following the correct order of the cards), and fix any problems that stop the user from progressing in the lab.
Add any explanations you feel are missing as you go through the lab.
Add better(more explanatory) visuals. For example, use diagrams to show/illustrate concepts and use picture of the output of the code to show students how their output should look like if they are correctly following the lab.
Goal: QA
All Cards