You can only add one logo to your sales invoices, BlondeAccountant.
At this time, QuickBooks Online allows you to add only one logo to your sales invoices, and placing an additional logo at the bottom of the form is unavailable. In your case, you can still customize your sales forms by including specific details to align with your school's standards in the Add payment details and footer sections. Within these sections, you can adjust the font size and position of the text to suit your needs.

For step-by-step instructions on managing logos in QuickBooks, check out this article: Add, customise, or remove logos on sales forms.
Also, I encourage you to share your feedback regarding this feature. Your suggestions help our engineers enhance QuickBooks and align it with your business needs.
Please let me know if you have other questions about managing the logo in QuickBooks Online (QBO). I'm here to help.