Adding -ing, -ed, or -er to a word sounds simple until the spelling changes: run becomes running (double the n), but jump becomes jumping (no change at all). Here are the 3 rules that predict which happens, with word lists sorted by pattern for practice.
Rule 1: Just add it
Most words need no change at all — this covers the majority of cases.
Rule 2: Double the final consonant
When a short word ends in one consonant right after one short vowel, double that consonant before adding the suffix — see our 10 spelling rules guide for the full explanation of why.
Rule 3: Drop the silent e
When a word ends in a silent e, drop it before adding -ing or -ed (the e's job — making the vowel long — is no longer needed once the suffix is there).
A quick word-sort activity
Write 12-15 base words on cards, mixed across all 3 rules. Have your child add -ing to each and sort the results into three piles: "no change," "doubled," and "dropped the e." Sorting by the pattern, not just reading the answer, is what makes the rule stick.
Suffixes are one piece of morphology — see prefixes and suffixes for the meaning-changing kind, and plural rules for how -s and -es work specifically for plurals.