I have an High School and a Ladies Guild that is associated with said high school. They report under the same EIN. (the High School's) There were transactions to both "entities" the High school's transactions added up to over $10,000 and then the ladies guild transactions totaled about $3000. Would I include the ladies guild transactions as aggregates to the high school? Would I report a "Person on whose behalf transaction is conducted" for both the High School and for the Ladies Guild or do I just report the High School?

First question to be asked. Is the high school a local government entity that can levy taxes and is therefore a Phase I exemption making the CTR question moot?

It is not a public school. It is a Lutheran High School that I believe would not qualify for that exemption.

I concur. An entity is never listed in Part I more than once. If the high school has permitted this organization to use its Tax ID number, I would file one Part I on the high school and list the Ladies Guild as an assumed name.

Ohhh...in the "alternate name" field in the Part I entry. That totally makes sense. I was kicking that idea around but it just seemed like it should be more complicated than that. I like your answer though.
Thank you for your help!

Just a suggestion, look at the EINs used by other groups and organizations associated with the school; .e.g band boosters etc. If they all use the school's EIN, it's more likely than not that they are all wrong. (If the funds are not controlled by resolutions from the same bunch of people who issue resolutions authorizing the opening of the school's accounts and naming of signatories they should not be using the school's EIN.)

If you correct this problem, any issue of aggregating goes away unless the funds are deposited by the same person.

That is an excellent point, Ken. I shudder to think of the confusion that would create and the hours that would have to spent sorting it all. Then you have the customer who probably wouldn't be to willing to get their own EIN for the separate groups....but I totally see where that would be the correct way. A lot of upfront work but the rewards would be felt later on for sure. Thank you for the insight.