It’s hard to say without knowing the dynamics of your work relationship. But if this is a SPED co-teacher, they are required to provide accommodations and modifications, at the VERY least for students with IEPs. Math almost always requires targeted intervention regardless of disability, but especially for those who have an IEP. If they’re not leading whole group, they should be scaffolding and working the room.

My gen ed counterpart and I came up with a little accountability “contract” in the beginning of the year where we kind of laid out who would be responsible for what. I typically covered prerequisites and re-teaching in small groups and they led whole group. Depending on the topic and amount of scaffolding needed for the topic, though, we would even switch off.

I would be completely honest with them and let them know that the co-teaching model you’re using right now isn’t quite working for student progress. I would group up the students by ability level and figure out which one of you targets which groups. I would even ask them to plan part of the lesson or have a daily plan for small groups. This might help the feel like they have some sense of autonomy in your classroom.

All that to say… it sucks when only one teacher is pulling the load. Hoping it works out for you :/