Surveillance data- finding counts of 2 or more cases in past 14 days

I am working with school health data (ie: new cases of people infected with a virus) and I have the data stored in line lists that generally have the following columns:

Name Student or Staff Grade/Classroom Home City Date of onset


What I'm trying to do is figure out the formula or commands that will allow me to count how many classrooms have had ≥ 2 positive cases in the past 14 days (rolling). I have very limited excel experience so apologies in advance if this is a simple fix. Also, if this is not enough information or confusing, please let me know. Thanks!