Thank you both for your help. I'd done everything with JavaScript so far, so I tried Bruce's answer and it worked perfectly!

I'm trying to have the value of a text field in a repeating subform (lets call it the “Identify” subform) of my form to be set to the value of “TextField18” in the corresponding subform instance of the “Groups” subform.In more detail:In the form I ask the question - how many groups do you have? The ...