My first-grade teacher made me write with my left hand. It wasn't until partway through the year that my parents discovered I was writing with one hand at home and with the other at school, and intervened.
I have no idea why she did this. My older brother is a lefty; perhaps she thought that meant I should be one too.
The possibility also has occurred to me from time to time, especially when my stutter is especially bad, that maybe she actually succeeded: that I actually was left-handed, but she managed to convince me that I was right-handed.
Mrs. Hlavsa was a witch. (No offense to Wiccans, past or present.) All I remember clearly about this particular issue is that one night at dinner my father had me write something with my left hand, and then with my right hand. After that he asked me which hand I preferred to write with, and I chose my right hand. That could be because I was right-handed, or it could be because Mrs. Hlavsa had me convinced that was the hand I was "supposed" to write with.
I mean what I said, though: She has got to be the all-time worst teacher I've ever had. It took me until last year to admit, however begrudgingly, that I do owe her some modicum of gratitude for teaching me how to read.