Time in the classroom
Time zones, the two clocks, and the seam in the calendar. Then, if you need a countdown, the timer is still here. Free, no sign-up, nothing installed. Part of the classroom hub; the full catalog is on lesson plans by topic and grade.
What this is
A time zone is a political stripe painted on a rotating ball. That sentence is the whole subject, and it is why this page starts with a map rather than a clock: noon is not a number somebody chose, it is where the sun is overhead, and every zone is an argument about how far from that a country is willing to sit.
The countdown timer is at the bottom of this page, where it belongs. It is a good timer and a lot of classrooms use it — but it is a piece of furniture, not a subject.
Submit a lesson plan Or send the questions your class asked →
On the projector
Everything here is already built. Open it, full-screen it, and teach.
Four lessons you can run tomorrow — no prep, no new tools
Run one of these and it worked — or didn't? Tell us, or send us your version: the written-up plan that comes out of it carries your name.
Lessons that run on them
Timed, step-by-step, every step a link that opens the exact view. One so far in this subject, and the full grid has the rest.
One full timed plan so far — which is exactly why this subject leads the list on the submission page. If you teach time zones, the two clocks or the date line, your lesson is the one this shelf is missing.
What we're considering building next — help us choose
None of these exist yet. Each would be built the way everything here is built — free, in the browser, computed from the real motions — and the class whose ask gets one built is credited on the page it becomes:
Vote, or ask for your own Or send a lesson you already run →
And when you do need a countdown
A visible countdown does the managing for you: it makes the length of a task explicit, it ends an activity without anyone being told off, and it turns "two more minutes" from a negotiation into a fact on the wall. Both tools have a full-screen mode, which is the point at which a timer becomes readable from the back of a room, and the time left also appears in the browser tab title.
Keyboard control, so you're not hunting for a button
Rotations, fluency and repeated trials
The timer runs up to three countdowns at once, each with its own label and its own alarm sound — enough for a three-station rotation where every group is on a different clock. For reading fluency or a repeated experiment, the stopwatch's Lap button gives a numbered list with each lap time and the running total, fastest in green and slowest in red. Three stopwatches on one screen lets each group have its own, named and coloured so they can find it from across the room.
A session leaves the page two ways: CSV (a row per stopwatch — its name, a column per lap, then the total) for records, and Share, one image of the whole session, for people. Both are named for the date and time, so a term's files sort themselves. Nothing is uploaded.
What a browser timer can't do
- It rings only while the page is open. The tab can be behind another window, but if it is closed or the machine sleeps, no alarm.
- A background tab may be updated less often by the browser, so a display that isn't on screen can lag.
- The precision depends on the device. Fine for classroom work — not for official sports timing, scientific measurement or anything medical.
- Sound needs the volume up and, on some browsers, one tap on the page before audio is allowed. Test it once on the classroom machine.
The full browser limitations page explains why, and the measured accuracy figures show how far off a browser timer actually is.
Accessibility — what to check
- The big read-out is drawn as segments rather than text, so it carries a text version for screen readers. It is deliberately not announced on every tick, which means a screen-reader user gets the value on demand rather than a live countdown.
- At zero the timer does three visual things as well as ring — the read-out turns to the accent colour and flashes, Time's up! appears under it, and the tab title changes — so a deaf or hard-of-hearing student watching the projector gets the same signal at the same moment. It does not vibrate, and the flash is the display rather than the whole screen, so full-screen it on a projector.
- Every control is a real button and reachable by keyboard.
- The display colour can be changed on the alarm clock and the timer if the default is hard to read on your projector.
Classroom timer FAQ
Does the timer keep running if I switch tabs? It keeps counting, but it can only ring while the page is still open — the tab can be in the background, the window can be behind another, but the page has to be there. If the laptop sleeps or the tab is closed, the alarm won't sound. On a classroom machine, leave the timer tab open on the projector output.
Can I run more than one timer at once? Yes — up to three at the same time on the timer page, each with its own length, its own label and its own alarm sound. That covers a rotation where three groups are on different clocks.
What are the keyboard shortcuts? On a timer's own page: Space starts and pauses, R resets. On the stopwatch: Space starts and stops, L records a lap, R resets. The multi-timer board on the main timer page is click-only — the shortcuts live on the single-duration pages.
How do I get the lap times out of the stopwatch? Two ways: CSV saves a spreadsheet that opens in Excel, Google Sheets or Numbers — one row per stopwatch, a column for each lap, then the total — and Share builds a single image of the session to send or save. Both files are named for the date and time you took them, so a term's worth of them sorts itself. Nothing is uploaded; the session lives on that device.
Is it accurate enough for a science experiment? For classroom work, yes — it times to a hundredth of a second. It is not calibrated equipment: the precision your device actually shows varies by browser and machine, and a background tab may update less often. It is not suitable for official sports timing, scientific measurement or anything medical.
Can I use the astronomy simulators on a projector? Yes — both are full-width and run in the browser with nothing installed. The Sun, Earth & Moon simulator has a page for every city, so you can open the one for your own town, and the location, date, time and span are all in the URL, which means one link puts every screen in the room on the same sky. Both carry a scale card explaining exactly what the drawing gets wrong, which is worth reading out loud.
Do I need an account? No. There's no sign-up and nothing to install — it runs in the browser, and anything you save (a running stopwatch, its laps) stays on that computer.