From the rehearsal room to the arena: how 100,000 children practise for 6K UNITED! with cori

Picture a sold-out arena (say, the SAP Arena in Mannheim, the Olympiahalle in Munich, or the Barclays Arena in Hamburg), with 6,000 singing primary-school children inside, backed by an 18-piece band. That's 6K UNITED!: a project founded by Prof. Fabian Sennholz that brings together more than 100,000 children from over 1,500 schools and choirs across Germany every season.

Since May 2026, every child in a 6K choir can practise for the big concert with a dedicated area inside the cori app. It's free of charge, and built specifically for children aged 7 to 14. This post is about what's actually in that practice area, and how the partnership between cori and 6K UNITED! came about.

But first: the problem.

A 6K choir, like almost any school choir, gets one hour a week. The children learn most of a song in that hour, then go home, and for six days the song lives nowhere they can reliably find it: a YouTube link buried in a parent WhatsApp group, a printed lyric sheet folded into a backpack, a "we'll come back to it next week" that quietly becomes "let's start that song over."

How a 6K year actually runs

A bit more practical context before we get to the app. Schools and choirs register with 6K, get a songbook, choreography videos and access to teacher workshops, then spend the school year preparing the same repertoire as every other 6K choir in the region. In May or June, all of them meet in the arena (Munich, Düsseldorf, Hamburg, Berlin, Mannheim, Hannover, Vienna) and sing a full concert together with the 6K band on stage.

The repertoire is a mix that surprises people the first time they hear it: recent German pop (e.g. Lotte's Mehr davon, Blumen und Beton from the Schule der magischen Tiere soundtrack), folk songs like Du, du liegst mir im Herzen, and the occasional classical line. Ode an die Freude turns up regularly. The whole thing is designed to work even if the teacher leading the choir has no formal musical training.

How the partnership came about

The videos and songbooks already existed. What was missing was a place where a nine-year-old could find them again on a Sunday afternoon, and a reason for them to come back on Sunday evening. Practising at home has the same underlying problem as homework: without a teacher in the room, the external nudge is gone. We wanted to build in some small, visible progress that says "You practised today, come back tomorrow." Something that keeps the arena concert alive in the children's heads, without anyone having to remind them.

A few meetings turned into a working prototype, and since May 2026 there's been a 6K area inside cori, included in every participating choir's 6K registration. 6K funds the development of that area through the partnership, and for participating choirs it stays free.

What's actually inside

Children get an access code that drops them straight into the 6K area. Three functions are worth describing in detail.

Practice videos, with live lyrics and jump markers

In cori, every 6K song has its own practice screen: the choreography and vocal video, the lyrics running live and highlighted on the line being sung right now, and jump markers to the sections a teacher actually refers to (warm-up, left-hand choreography, right-hand choreography, verse, chorus, bridge). "Practise the chorus of song 3 tonight" works as homework, because the child taps Chorus, lands there, the lyrics scroll along, and they can sing straight away, no pausing and rewinding.

It sounds like a small thing. From the conversations we've had with teachers, it's the feature that comes up first.

Interactive exercises

For some of the 6K songs we've built interactive exercises. The child sings along, and the app shows back immediately whether the pitch is right and the rhythm is sitting. No grade, no score: just a visible trace where the child can see where they are and where they still need to go. The analysis runs entirely on the device. The microphone signal never leaves the tablet or phone.

An interface designed for children

The features and the interface of the regular cori app have been adapted for the 6K area to fit children. A child opening the app sees a list of songs, a video and a streak counter. No member list, no audio mixer, no settings menus, no "tap here for more options".

If a child has to ask a parent how the app works, they won't use it when they're alone. And alone is the moment most of the practice has to happen in.

What was important to us in the work with 6K UNITED! and in shaping the children's area:

• No voice recording from children. Where sing-along features for children exist at all, the processing runs on the device, and the audio never leaves the tablet or phone.
• No personal features. No chat, no public profiles, no shared playlists between children. The 6K area is a closed practice room inside the cori app, with a single, clear purpose.
• No advertising SDKs, no third-party analytics tied to identifiable users. The app contains no ad networks. The 6K area is free for participants because the partnership funds it, not because behavioural data is being sold in the background.
• No accounts or email addresses from children. The child enters the code and starts practising. Parents install the app on the family device; nothing more is required of either side.

All data is hosted on German infrastructure. These standards aren't specific to the 6K area, by the way. The regular cori app, whether used as a choir management app, a digital practice room or a between-rehearsal practice platform, also processes data in line with GDPR on EU servers, with no ad networks and no sale of behavioural data. The 6K area additionally drops everything that works fine for adult choirs, like voice recordings, member lists and social features.

Getting set up

If you're a teacher or choir director with a 6K access code already in your inbox:

1. Download cori.

   

2. Enter the 6K access code on first launch.

3. Pass the same code to the parents of the children in your choir. They install the app on the family device the child uses for school work, enter the code, and land in the 6K area.

There's no account-per-child setup and no email collection, because there's nothing to collect: the code is the only thing that links a device to a 6K choir's content.

Detailed questions (devices, privacy, what's coming next) are answered on the 6K UNITED! in cori page.

What changes in rehearsal

I'm wary of strong claims about how much an app can change a rehearsal. What teachers in the pilot have told us, paraphrased: the hour doesn't get longer, but more of it gets spent on actual music instead of re-teaching what's been forgotten since last week. A Friday warm-up shifts from "let's remember the second verse" to "let's get the dynamics right."

A short note for choir directors outside 6K

The 6K project is the largest single deployment of cori to date, but the underlying observation, that the gap between rehearsals is where most progress is won or lost, applies to almost every choir we talk to. If you direct a regular youth or adult ensemble and you've been thinking about this, the cori feature overview is the right place to start. The same building blocks, the same GDPR-compliant data processing on European servers, just without the children-specific scaffolding.

Questions about the partnership, about setup for your own choir, or about cori in general go to info@getcori.app. We typically respond within one business day.

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More on this partnership: 6K UNITED! in cori | About 6K UNITED!