Dear [Name],

I hope you're having a good summer! 

I coordinate the [NAME OF MTC] Math Teachers' Circle at [HOST INSTITUTION], and I was wondering if you would be interested in guest-leading our circle sometime this [FALL/SPRING/ACADEMIC YEAR]? We hold regular meetings for math teachers to get together, share a meal, and do math together. As a guest leader, you could speak on a topic of your choice, or pick a math problem to work on with the teachers. (There a lot of resources for leading math circles on www.mathteacherscircle.org/resources/math-sessions/.)

Our circle meets at [TIME] on [SECOND TUESDAYS] at [LOCATION]. We also meet on selected Saturday morning. The dates we have available are below:

Date 1
Date 2
Date 3
…

Please let me know if this might work for you. [We're happy to provide travel reimbursement and a stipend].

Thanks in advance. I hope you can join us!

Best,
[NAME]