You could perhaps make a double set of sight word flashcards and play memory with them. Turn it into a game. If he turns over my and finds my again he then has to say the word to get the point.

You said that you printed sentences. Perhaps get him to help you cut up the sentences so they are just single words and then put them back together.

A lot of sight words are also difficult to learn if you dont know your sounds, even though they are called sight words and the idea is to know them from sight without sounding them out. So maybe work on the initial sound first.

If you have magnets he can also make the words with the magnets and then say them as he goes.

Painting the words can also help. So can writing them in a sandpit. Anything like that.

They all learn differently so if you can find one method that he enjoys that would be great.

I hope all that makes sense. If I think of other things I will add later.

All the best.