DS in 3rd grade has to get 19 out of 20 right before he gets the harder words. My sons biggest problem is, he goes too fast and will leave out a letter. When he gets home I will ask him to spell the word and he does it correctly.

We get the harder words list as vocabulary and I have him learn to spell them all.

When the test happens I have him do the harder words as well as the regular words. So he ends up doing 30 words every week. It's not perfect, but it works for now.