From our general experience, most teachers are decent at differentiating one grade up and one grade down. More than that and you get into grey areas. For example, elementary teachers don't get a lot of training in how to teach math. It seems basic enough that training programs just assume they can figure it out. But when you add in a hypothetical 3 years differentiation (in my son's case) and a newfangled Everyday Math textbook with an unmotivated teacher- you often get a whole lot of.... nothing.
Have a meeting and see where it goes! But don't sign anything! This is my advice in general to parents. Take the conversation (or notes or forms whatever you have!) home with you and think it over. Then send a thank you note. But if they ask you to sign anything before you leave, politely decline. I've seen too many principals, Special Ed coordinators and GT coordinators try to get parents to sign a formulaic plan so they can later say "but you agreed right here to give it a year!"
