It's free! Zearn allows your child to work on meaningful and engaging grade level tasks with guided support. Your child may already have a school account. Reach out to your child's teacher.
It is not free, but Tapestry has created an account for every child. Reach out to your child's teacher. IXL allows you to have your child practice specific skills with guided support.
There is a free and paid membership. The free membership has students practicing on grade level skills and offers support.