After college I started a tutoring business I called Math = Fun. I had become the go-to girl for my friends in high school who struggled with Algebra. (I lost that reputation when I almost failed Geometry...and Trig was no picnic, either.) I remembered how great it felt to be able to remove a friend's cloud of confusion.
I started my tutoring business with grade school students. My mission was to help end their struggle with numbers and begin to see the fun in math. At first I just helped them with their homework or had them do worksheets of problems to help build their math muscles. But that got boring, and un-fun, very quickly. So we moved on to games. I infused math into their favorite games like Monopoly and Trivial Pursuit. They loved it! They lost their fear and anxiety of math and just did it. And the more they did it, the more they could do.
Since that time, I've taught many students from grade school students through adults. Through these experiences, I found that explanations were great, but FUN was even better. Of course, students have to understand the math first or the fun won't happen. It would be like not being able to get past level 5 of a video game because you don't understand the game's tools or strategies -- supremely frustrating. But adding an element of fun seems to make the understanding come a bit easier.
From my non-researcher perspective, fun helps lift the "I can't do this. I hate this!" chat that continually plays in some students' brains. The more failures they have experienced, the louder this chat is. My relatively few bad experiences with math through my schooling days contributed to that chat. I'll still hear it from time to time when I am faced with a math problem above my level of understanding in a situation that is NOT fun. But give me a game, and I'll keep at it until I eventually learn it.