Krillion in the Classroom: A Free Vocabulary and Category Game

Krillion is a free category game that works well as a vocabulary exercise. A prompt such as "Name a musical instrument" appears, a clock runs, and the rarer a correct answer is, the more it scores. The student who types "piano" earns a little; the one who reaches for "bassoon" or "sitar" earns more. It runs in a browser with no sign-up and no student accounts, and a private room puts the whole class on the same prompt at the same moment.

That reward structure is the useful part. Most quizzes pay for the one right answer. This one pays for range: how many words a student can reach in a category, and how far past the obvious they can go. Below is why that matters, a 15-minute lesson plan, settings by age, notes for ESL classes, and the room rules to set before the code goes on the board.

"Name as many animals as you can in a minute" is one of the oldest tasks in language research, known as semantic or category fluency. In children it tracks vocabulary closely. A 2024 study of children and adolescents in the Journal of Communication Disorders found that fluency scores across ages, and between monolingual and bilingual children, largely mirrored differences in vocabulary size, closely enough that the authors explored using the task to estimate how many words a child knows.

Research on how people do the task is just as useful in class. Troyer, Moscovitch and Winocur, writing in Neuropsychology in 1997, split fluency into two parts: clustering, where you name items inside one subgroup (farm animals, then more farm animals), and switching, where you jump to a new subgroup (sea animals, insects). Strong performers do both. Switching is a strategy you can teach in a sentence, and it is exactly how a student finds the rarer answers Krillion rewards.

The game also gives students retrieval practice, pulling words out of memory rather than reading them off a list. In a well known 2006 study in Psychological Science, Henry Roediger and Jeffrey Karpicke had students either recall a passage or study it again. A week later, the recall group remembered 56% of it and the restudy group 42%. Producing a word under a little time pressure does more for it than seeing it again.

The rare words are also where most of the answers are. In our analysis of Krillion's prompt banks, only 5.3% of accepted answers sit in the bottom tier, Plankton, while 14.7% are in the top tier, One in a Krillion, and over half are Rare or Deep Cut. A prompt accepts 137 different answers on average. The game is a standing invitation to use the words students recognise but rarely say.

You cannot choose the prompts: the game deals them, and every room gets its own. So use the paper warm-up for your own topic and treat the dive as open practice in category thinking.

1. Minutes 0 to 3, paper warm-up. Write a category on the board that fits your unit, such as "Name a job" or "Name something in a kitchen". Students list as many as they can alone in 90 seconds. Then ask for counts, and have each student circle any word nobody else in the room wrote.
2. Minutes 3 to 5, open the room. On the projector, open the Krillion game, press Play multiplayer, choose Create a room, and set it to private with 7 prompts and 30 seconds. Write the six-digit code on the board. Students open playdaily.org/krillion, press Play multiplayer, type a name and enter the code.
3. Minutes 5 to 12, play one dive. After each prompt's clock, the reveal shows every answer in the room and its tier. This is your discussion. Pause on a Deep Cut and ask the student who gave it what it is. Ask the class which subgroup a rare answer came from, so switching becomes visible.
4. Minutes 12 to 15, follow-up. Show the podium. Each student writes three new words from the reveals in their notebook with a short definition, then uses one in a sentence as an exit ticket.

For homework or early finishers, a solo classic dive is 7 prompts at 25 seconds each, a few minutes of play.

A room can run 5, 7, 10, 15, 25 or 50 prompts, with 5 to 60 seconds to answer, and holds up to 75 players, enough for two classes together.

• Ages 8 to 10: 5 prompts, 60 seconds, in pairs on one device: one thinks aloud, one types. The prompts are general knowledge written for adults, with film, brands and history among the categories, so pairing helps when a prompt is out of reach.
• Ages 11 to 14: 7 prompts, 30 to 45 seconds.
• Ages 15 and up: 10 prompts, 25 seconds, the pace of a solo classic dive.
• Bell-ringer: 5 prompts, 20 seconds, done in a few minutes.

There is no speed bonus. Time only breaks ties, so a slower typist with a better word still wins the prompt, which matters with younger classes.

The prompts and answers are in English, which makes a dive a natural production exercise for English learners. The 2024 study above is directly relevant: bilingual children's fluency in each language tracked their vocabulary in that language, so category rounds aim at exactly the gap a learner is trying to close.

• Slow the clock. Give lower levels 45 to 60 seconds and pre-teach the category word ("utensil", "profession") before the dive.
• Mistakes cost nothing. A word the game does not accept is refused, not penalised, and the student can type again while the clock runs. That makes it a low-stakes place to try a spelling.
• Mine the reveal. Copy the rarer words from each reveal onto the board. That is a word bank built from your own students' answers.
• Flip it for beginners. Our sister game Noillirk rewards the most common answer instead, so a beginner who names the everyday word scores best.

There is nothing to sign up for and no accounts at all. Students open the page, type a display name and play. Nothing to set up, no class roster to import. It runs in a browser on laptops, Chromebooks, tablets and phones. A private room never appears on the public list, and the code works while the room is in use.

Because the display name is all others see, decide the naming rule before you start: first name and an initial, or a nickname you assign. Never full names.

Rooms have chat, and everyone in the room can read it. Lines that trip the game's language filter are not sent at all, and each student can hide the chat on their own screen, but set expectations anyway. Read these out before the code goes up:

• Use the private room code only. Public rooms are open to anyone on the internet.
• Names are first name and initial. No one else's name, and nothing you would not say to a teacher.
• Chat is about the game. Be kind about other people's answers: everyone's are on screen at the reveal.
• Do not call out answers during the clock. Everyone has the same prompt, so a word said aloud is a word handed to the room.
• Do not share the code outside class.
• The shop, where depth earns tokens for krill avatars, is for after the lesson.

For more on fitting short games into lessons, see our teachers' guide to brain games in the classroom.

Ten minutes of preparation is enough. Play one solo dive of Krillion Unlimited to get a feel for the prompts and the tiers, then make a private room and join it from a second device to see what your students will see. After that, the code on the board is the whole setup.

Roediger, H. L. and Karpicke, J. D., Test-Enhanced Learning: Taking Memory Tests Improves Long-Term Retention (Psychological Science, 2006).

Troyer, A. K., Moscovitch, M. and Winocur, G., Clustering and Switching as Two Components of Verbal Fluency (Neuropsychology, 1997).

Journal of Communication Disorders (2024), semantic fluency and vocabulary size in children and adolescents.