If you asked teachers in March, it's time to confirm they're committed and have what they need.
Dear [Teacher],
Thank you again for agreeing to write my recommendation letter. I wanted to confirm you received my brag sheet and let you know I'm planning to apply to approximately [X] schools, with deadlines starting in [early November/January].
Please let me know if you need any additional information from me.
Thank you so much for your support!
[Your name]
A lukewarm letter is worse than no letter. It's better to politely say:
"I understand you're very busy — I don't want to impose. I'll ask someone else instead."
This is your final chance! Popular teachers fill up quickly.