Bonus letters are consonants f, l, s, z   that are doubled at the end of a word with only one vowel in the word. I have found a video on YouTube that has a creative way of showing when to double the consonant, or adding a bonus letter. In class, we put a * above the bonus letter.  

                             

                                  *

For example:   s t u f f       

The star goes over the second consonant, or the bonus letter. 

 

This can get tricky for kids, so if you would like to share this video with them, I think it would help out.