Why can students do lessons that are not assigned to them?
Edited
Tynker student accounts give students access to both the Tynker for Schools dashboard and Tynker for Home dashboard all in one account, accessible via the School/Home mode button. Tynker for Home offers premium content (including Minecraft activities) that parents can subscribe to so their kids may further enhance their creativity and engagement outside the school setting.
See the student dashboard experience for additional info.