The AI tutor
Castor — a tutor that's already worked the problem
Grounded in each problem's worked solution and the NCEES Reference Handbook — the same document you'll have in front of you at the testing center.
How it works
Grounded, start to finish.
Stage 1
An authored problem
Every problem in the bank is original and written to the exam's own blueprint — the same areas, the same depth of calculation, the same Handbook dependence you'll face on exam day.
Stage 2
A reviewed worked solution
Before a problem goes live it carries a worked solution — the governing relation, the intermediate values, and why each wrong option is wrong.
Stage 3
Castor answers from that solution
When you ask Castor anything, it teaches from that worked solution — purpose-built on frontier AI, scoped to the problem in front of you.
- 01 — NCEES Blueprint
Mapped to the real exam
Pinned to an NCEES area and its exam weight, matched to what the real exam tests.
- 02 — Original
Original to CastorPrep
Purpose-built to exercise the exact engineering methods your exam tests.
- 03 — Worked Solution
Solved and checked
A step-by-step solution — every answer and distractor recomputed before it ships.
- 04 — Handbook Ref
Cited by section
Tied to the exact NCEES Reference Handbook section the method comes from, wherever the method has one.
- 05 — Grounded AI
Grounded help
Ask why you're wrong, get a hint, or have a concept explained — figures and exhibits too.
What it does
Three jobs, done properly.
Explains your miss
“You picked B — here's the step where B diverges.” Castor names the specific error that produces each wrong option, because the authored solution records it.
Cites the Handbook section
Every reference points at the section you'd flip to on exam day, so those references double as reps at finding the value under closed-book CBT conditions. Castor cites a section wherever the problem carries one.
Talks you through when stuck
Before you answer, Castor works in coach mode: it probes your setup, checks intermediate steps, and hands out graduated hints — one nudge at a time — while the final call stays yours.
Castor— AI tutor
Coach mode, before answering — a composite wall section: find the temperature at one layer interface.
Start by identifying what you're looking for and what you know. You have the two air temperatures, the total wall R-value, and one specific plane you need: the interface between the insulation and the gypsum board.
The key insight: temperature doesn't drop uniformly through a composite wall — it drops in proportion to the R-value of each layer.
So the first move is to identify which resistances lie between a known temperature and the plane you're asked about. Which end of the wall — indoor or outdoor — is closer to that interface?
Exactly right — the room air is your known reference point, and it's on the same side of the interface as the value you want.
Now: what layers sit between the room air and that interface? Read the wall section from the inside out. Start at the room and move outward until you hit it. Which material layers do you cross?
Good. So you have R = 1.13 between the room air and your target interface. Now use the proportionality:
where \Delta T_{\text{total}} is the difference between the outdoor and indoor air temperatures.
Plug in your numbers and solve.
A real coach-mode exchange with Castor, on a live problem from the bank. The final call stays yours.
What it won't do
Castor won't do your thinking for you. Before you answer, it coaches — it won't hand you the letter. It's scoped to the problem in front of you and your own work, because a tutor that answers everything is just a chatbot, and chatbots don't get you licensed.
When you’re stuck
Ask on the problem in front of you.
Ask why your answer is off, ask for a hint, or ask where the method lives in the Handbook. Castor answers from that problem’s worked solution. What each plan includes is on the pricing page.