Teach your students the rules of suffixes, such as when to add "-ing" (present tense) and "-ed" (past or perfective tenses). This will help them to discern when to double consonants.
Discuss syllables. Show students how to divide words into syllables by writing several words they are familiar with on the board and placing lines between syllables. Children can also learn to differentiate between syllables by clapping on each "beat" of a word.
Teach students about putting stress on certain syllables and give examples, such as "earring" or "permit," showing students where the stress is in each word.
Give the students rules: Double the consonant before adding a suffix if a one-syllable word follows a consonant-vowel-consonant pattern, such as "run" or "pop." Also double the consonant if the stress is on the second syllable of a word.
Give your students a list of verbs. For homework, ask them to add "-ed" and "-ing" suffixes. Go over the work the next day in class to make sure they understand the concept.