When trying to join a Google Meet meeting using a G Suite Education/school account, you get the following error.

Error: You can’t join this meeting with your school account. Sing in with another Google Account and try again.

This is because G Suite for education users are only allowed to join meetings created by other G Suite users. If you try to join a meeting that was created by Gmail personal account you will get above error. Unfortunately, this is a limitation for personal account and to safeguarding put it in place for education users. Below is statement from official Google article on this.

G Suite for Education users

If you have a G Suite for Education account and your school type is Primary/Secondary education (K-12), you’ll not be allowed to join Google Meet video calls created by non-G Suite, or personal, Google Accounts.

Ref: https://support.google.com/meet/answer/9303069

Solution 1: Create the meeting using a G Suite account

This issue is happening due to meeting creator using personal account. Instead, if you create the meeting using your G Suite account, those users using the personal account can also join.

Solution 2: Access meeting using personal account(@gmail)

Since this issue is limited to G Suite Edu users accessing meeting created by a personal account, you can instead use your personal @gmail.com account to access the meeting without this limitation.