Please watch carefully your students’ workflow. As per the contest rules, the student may have only 1 task claimed at any point. Please be careful that your students are not un-claiming then re-claiming tasks after they have completed them, in order to do tasks in parallel. Doing so is a violation of the contest rules.
If you have questions or concerns, please contact me or @sunbiz via private message here, or offline.
You can see the workflow history by reviewing the time stamps and actions in the comments section of each task in Melange.