Source: Brilliant | Learn to think
A lot of the sites I link to have a lot of value at a the free tier. Although Brilliant does have some activities available for free, to get the most out of it you’ll need to subscribe. Also, the site doesn’t have any classroom management or school plans.
So why am I even mentioning it? Because you may have students that need either additional help or need to be pushed. Brilliant could be a site to recommend to parents. Check it out for science and math!