Why do these students look so happy? They've just earned T-shirts for playing Vocabulary.com.

At Houston's Chavez High School — which took home back-to-back monthly leaderboard wins in the Vocabulary Bowl in November and December — students are making word learning part of school culture and school pride.

And their level of engagement is taking even Chavez teachers by surprise. Last month, planning a Vocabulary.com Fest in the cafeteria to celebrate their November leaderboard win, English department chair Cristina Saldarelli expected 150 to 200 students to attend. Instead, 400 showed up to socialize and play Vocabulary.com, filling the cafeteria at the 3,000-student school to capacity. As a party favor, each received a snazzy "Vocabulaire Extraordinaire" T-shirt.

Celebrating their monthly leaderboard win, about 400 Chavez students gathered for a Vocabulary.com Fest.

How did the school create this buzz around vocabulary? "Competition," said Saldarelli. "Our kids talk about the competition all the time."

It's exciting that Chavez is neck-and-neck with local rivals Bellaire High School and Mickey Leland College Preparatory Academy for Young Men, but most of the competitive focus comes from within the Chavez community itself. "It's kids against kids," said Saldarelli. "It's kids against teachers. Whenever we talk about the rankings they perk up. The kids are proud to say they're at the top of the rankings and it's become a part of our culture. The game has fully penetrated the school community. There's a huge group of students that are highly engaged with it."

Competition was the factor driving teacher interest as well, Saldarelli went on to explain. "From the outset, I was really impressed with the program," she said, but teachers didn't quite grasp its potential until they saw that Chavez's initial play was putting the school up on the leaderboard. After that, teacher engagement took off, with English department faculty not only using it in their classroom, but reaching out to colleagues in other academic departments where a focus on vocabulary learning can be just as critical to student success.

Before Chavez adopted Vocabulary.com, there was no formal vocabulary program in place at the school, even in English classes. Like many schools, "we just had to make vocabulary work with our units and our lessons," said Saldarelli. Now, vocabulary learning is easy to make a larger and more integrated part of the existing lesson plans. "It's so great for us as teachers because we can find lists that apply to what we're learning or we can create them easily through the program and refer to that list in the future."

The flexibility also allows students to take charge of their own learning. "All students complete their class requirements, while those who have an intrinsic drive to further their learning are able to go beyond the expectations of their teachers."

The word-learning is already evident in the way students use and talk about language. Students in Saldarelli's classes now routinely engage in in-class conversations about words, and anytime a word that smacks of "vocabulary" comes up, there are immediate callouts from their peers of "Vocabulary.com!"

Saldarelli doesn't see the game's impact at Chavez as a passing fad. "It hasn't died down. The students would say 'It's so addictive I can't stop.'" Recently, during lunch, when two students who were working furiously against a deadline in Saldarelli's classroom learned the deadline had been moved, they followed up their excitement at this news with, "Okay, great, now we can get on Vocabulary.com!"

Students leading Chavez High School's monthly leaderboard victories in the Vocabulary Bowl include top scorers for November Jose Reyes, Richer Pham, My-Khanh Nguyen, Thao Dang, and Lesley Avalos, and the December top five Jose Reyes, Vivian Lopez, Christian Gomez, Ashley Valenzuela, and Jasmine Ward.