Verbs with -ing, -ed endings (Levels 9-3 and 9-4)
Levels 9-3 and 9-4 deal with verbs ending with -ing and -ed, some of which double their final consonant before the -ing or -ed ending. The words in level 9-3 are swimming, running, winning, throwing, washing, mailing, kicking, listening, hopping, and sitting. The words in level 9-4 are mixed, covered, enjoyed, compared, planned, tapped, dropped, tagged, stopped, and tipped. The general pattern here is that verbs which end with a short vowel + a single consonant will tend to have that final consonant be doubled when an -ing or -ed ending is added to the word.
Read more...