How do we cater to the diverse groups in a mixed-age classroom with 3 different grade levels?

I am in a mixed-age classroom with grades 6-8 together. We have a grade-level curriculum in place that must be completed during sessions throughout the term. The setup is a microschool, and I have only 1 learner in grade 6 and grade 8, but the majority are grade 7 learners. I want to understand strategies as an educator to cater to learners in a 40-minute session across the different topics in math at their grade level.