STEM
SplitForge
Enter your own swim/run/bike times (ages 9–14) and learn the middle-school ratio & percent core through them: pace as a unit rate, percent improvement, negative vs positive splits, yards↔metres, and qualifying cuts as inequalities. Five little coaches, each one math move. On-device — no names, no upload, no AI.
▶ Play it nowBuilt for sittings of about 20 minutes on the screen. That is our design budget, not a measurement.
Meet your mentor
Every Spark & Anvil app has a friendly mentor character that demonstrates, asks, and patiently scaffolds learning.
Mentored by Marlin
#1f7ea8 Characters who teach
Meet the cast
SplitForge's little coaching crew (ages 9–14): 5 coaches, each EMBODYING one ratio-&-percent move (the character IS the operation). Mentor = Marlin, the coach who reads the pace clock with you.
Split the Stopwatch
mixed-unit subtraction — the take-away between two clocks
Read chapter →
Pace the Penguin
the unit rate — your time shared out over every 100m
Read chapter →
Cut the Standard-Setter
the inequality — your time must be <= the qualifying cut
Read chapter →
Convert the Otter
yards <-> metres — a yard is a little shorter than a metre
Read chapter →
Taper the Tortoise
the season graph — your best, your average, your improvement
Read chapter →
Browse all chapters → · What's distributed-narrative methodology? →
What's inside
Learning goal
Enter your own swim/run/bike times (ages 9–14) and learn the middle-school ratio & percent core through them: pace as a unit rate, percent improvement, negative vs positive splits, yards↔metres, and qualifying cuts as inequalities. Five little coaches, each one math move. On-device — no names, no upload, no AI.
Mentored by Marlin — no data leaves the device.
How SplitForge handles your kid's data
- ✅ All progress, settings, and AI-generated content stays on the device
- ✅ No analytics, no tracking, no third-party SDKs
- ✅ Free — no ads, no in-app purchases
- ✅ No personal information collected from children — in line with COPPA (updated by the 2026 FTC amendments)
- ✅ No chat with strangers — play-together rooms use a short code and preset emotes, never typed messages
For you, the grown-up
The grown-up side of SplitForge on Spark & Whetstone, our free site for grown-ups: The Deck Clock. They predict the shape a send-off draws; you run the set on any screen.
It also tells what SplitForge teaches in a short course of its own.
SplitForge runs on ForgeKit — the open-source Swift Package Manager framework that powers every Spark & Anvil app. ForgeKit ensures consistent accessibility, COPPA compliance, and design language across the portfolio, so your kid's progress and preferences feel coherent across every app they touch.
Coming to the App Store
SplitForge is in active development. Email us to hear when it ships — no marketing, no spam, just a one-shot launch announcement.
Email me at launch