RTI (I’m assuming this is Response to Intervention)…is a regular education initiative. Some schools pay folks as tutors to do this. Where I am, any teacher doing this would need to be certified in the area in which they are doing interventions. There is no “test” to teach RTI in my state. So…here, to do this, one would need to be certified in literacy or math or science…or whatever content area RTI is being used for.
Frankly, a part time music teacher can likely earn a lot more teaching private instrument lessons if they are hired part time in a school.