If the learning site was Edmodo, I wouldn’t worry about it. I was a member at the time and they notified me promptly¹. To date, it’s the only account I have that’s listed on Troy Hunt’s “Have I Been Pwned?”² but I was impressed with how they handled it and reassured that the passwords were stored with the bcrypt algorithm.

1. https://support.edmodo.com/hc/en-us/articles/115007376848-Im...

2. https://haveibeenpwned.com/