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The SAT prep platform that behaves like the real test

Case study

NALA Prep is a digital SAT platform: 10,000+ practice questions, 30+ full-length practice tests, adaptive scoring, AI diagnostic gap-scoring, and a 24/7 AI tutor kept grounded in the material. We took over an existing codebase and rebuilt it, from the test engine to the billing.

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The NALA Prep test screen: a timed digital SAT Reading and Writing module with mark-for-review and four answer choices

Product: NALA Prep, a digital SAT practice platform
The bank: 10,000+ questions and 30+ full-length practice tests
Our role: Full-stack development: test engine, adaptive scoring, analytics, Stripe billing
The AI: Diagnostic gap-scoring plus a 24/7 AI tutor, grounded in the material

Inside NALA Prep

Diagnostic gap-scoring: every skill scored, not just the section
The embedded Desmos calculator inside a timed math module
Answer reports map every question to the skill it tests

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The hard part was fidelity to the real exam

Practice only transfers when it behaves like test day. Three problems decided whether NALA Prep felt like the real digital SAT or just another quiz app.

A simulation, not a quiz
The digital SAT is module-adaptive and strictly timed, with its own tools: an embedded Desmos calculator, mark-for-review, answer eliminations. Every piece had to behave the way it does on test day, or practice builds the wrong habits.
Scores that say what to fix
A section score tells a student where they stand, not what to work on. The scoring had to break every test down by skill and question type, so the next study hour goes where the gaps actually are.
An AI tutor that cannot bluff
Around-the-clock help is only worth shipping if the answers hold. The tutor stays grounded in the platform's own questions and explanations instead of improvising math, because a confident wrong answer costs a student more than no answer.

What we built

A full-simulation test engine

Timed modules, mark-for-review, and an embedded Desmos calculator: 30+ full-length practice tests that behave like the real digital SAT, over a bank of 10,000+ questions.

Adaptive scoring and gap-scoring

Scoring that mirrors the module-adaptive digital SAT, then AI diagnostic gap-scoring that breaks every result down by skill and question type.

A 24/7 AI tutor, grounded

Help on any question at any hour, with answers grounded in the material. The tutor does not improvise math; it explains from the platform's own content.

Analytics and subscriptions

A performance analytics dashboard for students, and Stripe checkout with recurring billing carrying the business.

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How we built it

Mirror the exam
We built the test-taking experience to the digital SAT's own rules: module timing, question tools, and the embedded calculator, so nothing on test day feels new.
Score it like the real thing
The adaptive scoring system reproduces how the digital SAT weighs a student's path through the modules, which is what makes a practice score worth trusting.
Turn results into a plan
Answer reports tie every question to the skill it tests, and the gap-scoring rolls that into a per-skill picture a student can act on.
Keep the AI inside the material
The tutor answers from the question bank and its explanations. An ungrounded model improvises; we built this one so it cannot.

Shipped full stack on React, Next.js and NestJS, with Stripe handling checkout and recurring billing.

The parts that were not obvious

The SSR bug that took real debugging

An obscure Next.js server-side-rendering failure on Fly.io took real debugging to pin down. It came with the territory: we took over an existing codebase and stabilized it while shipping features.

Recurring billing is a lifecycle

Stripe checkout is the easy half. Subscriptions renew, fail, retry and cancel, and every one of those states has to leave a student's access in the right place. The billing work was in the lifecycle, not the checkout button.

Fidelity lives in the small tools

The Desmos calculator, answer eliminations, mark-for-review, the timer's exact behavior: none of it is the headline feature, and all of it decides whether practice transfers to test day. We treated the details as the product.

The stack

React
Next.js
NestJS
Stripe
Fly.io

Where it landed

10,000+

SAT practice questions in the bank

30+

full-length digital SAT practice tests

24/7

AI tutor, grounded in the material

See it live: nalaprep.com

SAT prep platform development FAQ

How long does it take to build an SAT prep platform?

A production MVP typically takes 12 to 20 weeks. The test engine and billing move fast; the question bank tooling, the adaptive scoring, and the reporting depth set the pace. NALA Prep runs 10,000+ questions and 30+ full-length practice tests on that foundation.

What stack is NALA Prep built on?

React and Next.js on the front end, NestJS behind it, and Stripe for checkout and recurring billing, deployed on Fly.io. We took over an existing codebase and rebuilt it.

How does adaptive scoring work on the digital SAT?

The digital SAT adjusts the second module of each section to how a student performed on the first, and the score reflects that path. NALA Prep’s scoring system is built to track that behavior.

How is the AI tutor kept honest?

It is grounded: answers come from the platform’s own question bank and explanations, not from a model improvising math. That constraint is the difference between a tutor students can trust at 2am and a confident source of wrong answers.