When I was younger it felt scary to tell them. As an adult, I kick myself for being scared to tell them. They're just a human who should have the decency to understand speech impediments are something we can't change. It's like telling anyone else, "hey, I stutter, it is what it is!" For what it's worth, I never had a teacher give me any backlash. They didn't baby me because of it, but they didn't treat me differently either. And I had some real asshole teachers, but even they knew they can't actually discriminate against a child or teen with a speech impediment.