If he likes puzzles games, he could boost his vocabulary over the summer break and have fun beating his (and your) best times by playing Word Search Perfected. It's free, so give it a go.
I developed Word Search Perfected for my own kids (5 & 8). They enjoy it more than other similar apps. One key improvement is that there are different difficulty levels. The number of directions in which words are placed and the size of the vocabulary increase across the difficulty levels, so puzzles can be tailored to suit every ability. I even spent hours weeding out all the swear words from the 75,000-word dictionary, so parents don't have to deal with questions like, "What does ****** mean, Daddy?" My daughter and I like to play a puzzle together and see who's the quickest to find each word. We can also click on an unfamiliar word to look it up in a dictionary and find out what it means.
You can get Word Search Perfected from Google Play, Samsung Apps, Amazon Appstore, SlideME, and several other places.