In addition to and English teacher, I am also a dyslexia interventionist. The rules we use for the dyslexia intervention are as follows:
1) If the base word ends in an unvoiced sound, then -ed=(t).
2) If the base word ends in a voiced sound, then -ed=(d)
3) If the base word ends in the letter t or d, then -ed=(ed).
I hope this helps some more.
