Catrobat: more than block coding

What Catrobat is, and who is behind it

Catrobat is an open-source project developed at Technische Universität Graz in Austria. Pocket Code is its best-known result: an Android app that lets children build games and animations by snapping together labelled visual blocks instead of typing lines of code. It is free, and its development is run out of TU Graz as a community project rather than sold as a commercial product.

The visual-block approach puts Catrobat in the same family as Scratch, MIT's well-known children's programming environment: both replace text syntax with blocks a child can drag, connect and rearrange. That family resemblance is real. What sets Catrobat apart is not the blocks themselves but where they run, which is the subject of this article.

Pocket Code was the technical foundation this project built on.No One Left Behind funded a new generation of it and shaped a school-facing edition around it, Create@School, wrapping the same open canvas in templates and tasks a teacher could set inside a single lesson.

Why "runs on the phone" is more than a detail

Scratch, and most of the tools schools compare it to, run in a browser on a desktop or laptop computer. The child writes code on a machine sitting at a desk in a computer room, or, at home, on a shared family computer. Pocket Code is different in a way that is easy to state and easy to underrate: the programming environment itself is an app that runs on the phone. The device the child writes code on is the same device they run and test it on, and it is very often a device they already carry in their pocket.

For a school with a well-equipped computer room, that difference may not decide anything. For a school without one, or one that can only book the computer room once a fortnight, it is the difference between a coding lesson happening on schedule and a coding lesson being quietly dropped. The same logic applies at home: a family whose only shared computer is a phone is not excluded from Pocket Code the way it would be from a browser-only tool. That is not a minor convenience feature. It is what makes the tool usable at all in a room, or a household, with no PC in it.

Where it hits its limits

A phone screen is small. Arranging and rearranging more than a handful of blocks on a touchscreen is more fiddly than doing the same thing with a mouse and a large monitor, and typing labels or values on a phone keyboard is slower than typing on a physical one. Projects that stay simple, a short animation, a small game with a few rules, sit comfortably within that constraint. Projects that grow more ambitious will eventually ask more of a small screen than it comfortably gives.

There is also the question of the device itself. Pocket Code being an app on a personal phone means a school or a parent has to think about what that implies: whether the phone is school-managed or the child's own, what else is installed on it, and how much supervision a phone invites compared with a shared classroom computer that never leaves the room. None of that is a flaw in the software. It is simply a different set of questions from the ones a computer-room tool raises.

How it compares to Scratch

At the level of the block language, the two are close enough that a child moving from one to the other is not starting from zero: both use labelled blocks to control characters, motion, sound and simple logic, and both aim at the ideas behind programming rather than its syntax. Where they part ways is the platform underneath. Scratch is a browser tool built around a desktop workflow; Pocket Code is a native app built around a phone. Neither is more "correct" than the other. The right choice depends on what hardware is actually sitting in the room, or in the child's pocket, on the day the lesson happens.

What we have not tested

This site has not run Pocket Code across a range of Android phones to see how it behaves on older or budget hardware, and we have not compared its performance against Scratch in a classroom setting. We have not reviewed the app's current store listing, its ratings, or the specifics of which sensors or hardware features it supports on a given phone model. This article draws on Catrobat's own published description of the project and on the project's role in No One Left Behind, not on hands-on testing by this site. The published evaluation of the Create@School approach appeared in Sensors in 2019; we have read its title and authorship, not its findings, so we point to it here rather than characterise what it concluded.

Who should use it, and who should not

Pocket Code is worth a look for a school without a reliable computer room, or for a teacher whose pupils' most consistent access to a screen is a phone rather than a PC. It is also a reasonable choice for a parent who wants a free, no-account, open-source option rather than a subscription service with a mascot attached.

It is a weaker fit for a classroom that already has a computer room and wants pupils working on more elaborate, longer-running projects, where the larger screen and keyboard of a desktop tool will make the work easier rather than harder. It also assumes access to a phone in the first place, and a school or family with a strict no-personal-device policy will need to weigh that before choosing it. For a wider comparison across creation tools by age, cost and licence, see the tool hub.