Answer: Always stay with simple one syllable short a sound words until the student is very familiar and comfortable with simple one syllable words before going to multisyllable or compound words.
Example: Teach at words: at, bat, cat….
Then teach, ap sound words: cap, lap, map… Hold off on apple, happy, clap, or other ap sound words that are more than one syllable or combine multiple consonant sounds. Teach simple words first, then move up the ladder to more complex words. You are teaching students how to read, spell, and write words—all at the same time [see my blog on the 4-steps for 2/14/18] . So, keep it simple.
Next, teach an sound words: an, and, fan, ….
Teach am sound words: am, bam, ram….
Teach ad sound words: add, bad, fad, sad….
In this way, students get the idea that the vowel sound is staying the same, even when the consonant changes. Again, you want students to learn to work with words but not memorize. We are training the brain to recognize letter sounds, not memorize patterns or rules. Once you have established this principle with the student, and the student can read, spell, and write these simple words, then you are ready to move up to more complex words: an, and, sand, stand…
Some students will move up faster than others. Do not move up until the student is ready. Help students see how words change sound before teaching multisyllable or compound words: apple, happy….
You use this same approach for each vowel sound—step-by-step, but remember, teach all 7 sounds for the letter a before starting on the next vowel sound.
If you are interested in ready-to-use curriculum that teaches these principles, I do have a book available that I use with my workshops. Contact me.