I found this wonderful site that offers a fun way to improve kids spelling for free. Kidspell.com offers some 6,600 words to practice with. This way, when your child is already doing his own research for things he is passionate with, he won't be typing "skaetboard ramps" like this. After all, misspellings and typos affect the amount and quality of searched sites generated (although yes, Google often asks if we meant another thing).
But the surest way to practice a child's mastery of spelling is to do it with them in a fun way. Setting aside a spelling time with them might not always work, but going about the things you do together and spelling some of the words related to your activity should help more than you'd expect. You can even point out certain spelling and grammar rules without the pressure to learn during these times.
"See baby, the water is calm so we can go swimming without worrying about the waves. It's calm, c-a-l-m, and you pronounce it as kam because the L is silent or very light. It means there's no wind to disturb the water."