Why am i forced to do presentations even though i have a lisp and speech impediment?

I mean, all my teachers make me do them, And i sound like a total retard and idiot, so i always just do horrible on them. Since we're graded on the presentation and our fluency, and i always get terrible grades. I mean i know i have to improve but not IT's adding my shyness and problems, Thats like hell. Yet I am forced =/ I know i have to overcome stuff in life but It's not that simple. It's pretty much the worst thing ever if you have speech impediment then you would know.