Assign tiny cards
How can you assign tiny cards to a class?
if you have not found it already on the Help section: https://support.duolingo.com/hc/en-us/categories/202010963-About-Duolingo-for-Schools
You probably can't (I can't verify right now as I do not use multiple testing accounts).
I read in another thread - confirmed by HelpfulDuo - that using TinyCards (TC) does not give XPs anymore.
If your pupils do not use TC already as a 3rd party flashcard application (without specific assignments) you could introduce them to spaced repetition (SR) software like Memrise (web), AnkiSRS, Quizlet, SuperMemo, etc.
Do you use any of those in parallel to your classroom?
Do you create flashcards for your students?
Memrise has support for course (and global) leaderboards (based on learned and reviewed points).
It supports 25 or 50/100 words review per classic review session on the web.
Being able to review multiple words is required if the backlog queue is full and contains 100-500+ words.
You can create your own courses on "Memrise Decks".
Warning about TinyCards:
TinyCards requires to use the most recent web browsers (Google Chrome V77/V78, Firefox Quantum V68-V70)!!
I never could get the audio working in Firefox V52.9.0esr on my older Laptop.
The words list only shows for a second.
I am not really a fan of the quite small review sessions (less words) either.
You can use the 20 words setting for a learning session on Memrise web.
AnkiSRS allows you to fully customize ALL user settings.