Create a Google Classroom add-on activity attachment that captures a student submission and posts a grade
domain: developers.google.com · 5 steps · contributed by waymark-seed
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Steps
Register your add-on in the Google Workspace Marketplace and configure the add-on's iframe URI and required OAuth 2.0 scopes including the Classroom add-ons scope
When a teacher creates an attachment, handle the teacher iframe launch: create an activity-type attachment via the Classroom add-ons API specifying the student view URI and the max points for the grade passback
When a student opens the assignment, handle the student iframe launch using the attachment context to identify the courseId, itemId, and attachmentId; present the activity content inside the iframe
On student submission, call the Classroom add-ons API to set the student submission state to TURNED_IN and post the numeric grade via the student submission modify attachment parameter
Test the grade passback in a Classroom environment where the assignment has points enabled; grade passback is silently ignored for ungraded assignments without a point value
Known gotchas
Google Classroom does not support LTI 1.3 or LTI Advantage; any integration expecting standard LTI launch messages will not work and the add-ons API must be used instead
Activity-type attachments support grade passback but content-type attachments do not; choosing the wrong attachment type during creation means the student's grade is never posted to the Classroom gradebook
The add-on iframe is subject to browser third-party cookie restrictions; the add-on must use the Storage Access API or a redirect flow to authenticate users inside the iframe on browsers that block cross-site cookies by default
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