I respond: “you say, you can’t.”
I suggest, “you can’t YET and you can learn to.”
I may say, “You say you can’t and thank goodness, because that’s why I am here: to help you learn how to.”
I may say, “Show me what you can do and we’ll go from there.”
I may ask, “Exactly what is it that you say you can’t do?”
And then, “What would you like to do about that?”
Or “How can I help you with that?”
Later I may ask, “So how long have you been working on this?” (usually a matter of a few minutes). Therefore grounds for the next question: “How long do you think it might take to learn something like this?”
A reminder may be useful: “Do you remember when you learned how to … And now you can?”
Or I might admit: “You know what? I don’t know how to do that either right now. Who do you think could help us out with this?”

What I’ve learned from nearly two decades of teaching Physical Education: when kids tell us they can’t, they mean it. They are not making it up, they really feel like they can’t perform the skill, play the game the way that we’re asking them to do it at that moment. Whether it’s a temporary or habitual “I can’t,” we need to acknowledge that child’s reality first before offering strategies to get beyond “I can’t.”
Encouraging a growth mindset by adding yet to their negative statement as in “You can’t skip rope yet” plants that seed of understanding that this particular state is temporary (although some of our kids may feel like it’s forever). Open questions (i.e., starting with how and what) invite students to problem solve and become masters of their own progress and send the message that we see them as capable, creative and whole.
“I can’t” is also an opportunity to remind kids of past challenges and successes. I sometimes raise the rhetorical question, “so when you were born, did you already know how to walk?” This tends to put their current struggle into perspective, often with a smile.
Truth be told, I actually appreciate every “I can’t” ever heard from a student. It reminds me and my students just what we are there for: to create something new together: a new competency, understanding, a new way of seeing ourselves. We’re all growing and changing the whole time. Welcoming and working with those inevitable “I can’t” moments in the process only serve to deepen the potential learning.