Here's an intervention for spellers who are frustrated with words that don't follow the rules. I usually add one or two of these to each week's spelling list as "bonus words" or "challenge words".
Explain to the student that irregular, or exception words have a part that doesn’t follow the usual sound-symbol correspondence rules.
Many common words like said, are, and was, are examples.
Draw attention to the irregular part of a word by writing the letters larger and/or using a different color.
For example, in the word said, print the ai larger or in a different color.