The best AI tutors in 2026, compared by what they know about you

In 1984 Benjamin Bloom reported that students tutored one-to-one scored two standard deviations above a conventional class. The average tutored student beat 98% of the control group. The number came from two dissertations by his own PhD students, Joanne Anania and Arthur Burke, and it has not held up at that size. Kurt VanLehn's 2011 review put human tutoring at d = 0.79 and step-based tutoring software at 0.76.

An effect of 0.79 still moves an average student to about the 79th percentile, and a tutor has never been cheaper. ChatGPT, Gemini and Claude each ship a mode that asks questions before it answers. None of the three documents a record of what you understood yesterday.

I build Understand, a voice tutor for adults, so I have a stake in this comparison. Several of the products here beat mine at something, and I name it each time.

Method

I looked at five things for each AI tutor app: whether you can talk to it, whether it keeps a model of what you know, whether it teaches from your own material, who it is built for, and the price. Every price and limit comes from the vendor's own page, read on October 3, 2026, unless I name another source.

The short version

ChatGPT voice and Study Mode against Understand

Most people looking for an AI tutor already have ChatGPT. Study Mode is on every ChatGPT plan, on web, iOS and Android. OpenAI's FAQ says to turn it on by typing @study in the message box, or by opening chatgpt.com/studymode. The same FAQ says it "is not available in Temporary Chats, GPTs, or Projects". On memory it says ChatGPT "may use saved memories or past chats to personalize study mode". The launch post lists "goal setting and progress tracking across conversations" as future work, and the FAQ I read today still describes no such tracking. The FAQ mentions voice only as dictation.

ChatGPT voice mode is a separate feature. The voice FAQ describes Live, which runs on GPT-Live-1 and can listen and speak at once. Plus ($20 a month, per OpenAI) gets 3 hours in a rolling 24-hour period. The $100 Pro tier gets 15 hours and the $200 tier is unlimited. Free accounts get limited time on a smaller model. The same page says "Live cannot currently find or add files from your ChatGPT Library", though you may be able to attach a file to the chat by hand.

In Understand the voice does not teach. The teaching is done by a second model behind it, which reads and writes a record of what you know.

A model of what you know that you can read

Understand keeps a table of concepts and a table of evidence. When you explain softmax correctly, the tutor writes a row: the concept, the date, what you said, and whether you succeeded or struggled. A concept counts as something the tutor can build on only after two successes in two different contexts. If your latest attempt was a struggle, it goes back to "don't assume".

You can open this as a page in the app, called Knowledge graph. Concepts nest under their parents with a green, amber or grey dot. You can rename a concept, merge two, delete a note the tutor got wrong, or mark something "I know this".

Interest is stored apart from understanding. Say "skip the history" and the tutor marks the history of that topic as not interesting to you, without recording that you understood it.

ChatGPT's memory is a list of facts about you. You can review, correct and delete them, which is good, but OpenAI's own page says memory "does not retain every detail from every conversation". It has no notion of a concept you got wrong on Tuesday.

Read-aloud that keeps every sentence

Upload a PDF or save an article and Understand reads it to you word for word, sentence by sentence, with the current sentence highlighted. You talk over it. "Wait, why does that follow?" pauses the reading, the tutor answers, and the reading resumes at the same sentence. "Skip", "go back", "faster" and "summarize the rest" work by voice.

Ask ChatGPT's voice to read you a long article and it tells you what the article says. I asked it how much of the article it could see. It said it had a high-level summary, or the first few sentences. In a typed chat it did quote an uploaded PDF word for word when I tested it. For a paper I want to understand, I want the author's sentences and the right to interrupt them.

Understand reads only text. Scanned PDFs are refused and figures are ignored.

A saved list the tutor picks from

Understand is also a read-later list. A bookmark button in the app, a Chrome extension, the iOS share sheet and your X bookmarks all save to it.

Ask "what should I learn right now? I've got ten minutes" and the tutor looks through the list for something short enough and checks its ideas against your knowledge graph. Then it proposes one piece and names the idea in it that is new to you.

A board, imports and one tutor per subject

While it talks, the tutor draws on a board: an ASCII diagram, an SVG, a short definition, or a photo it searched for.

You can point it at your blog or your GitHub. It reads your posts and READMEs and records the ideas you wrote about as leads. An imported idea is never treated as understood. The tutor pitches higher and asks one check question first.

Each subject gets its own tutor with its own transcript and board. Ask about mortgages in the middle of a lesson on attention and the call moves to a Mortgages tutor without hanging up. Later, in any tutor, "what did you tell me about amortisation?" is answered from that other thread by full-text search.

Asking you to explain it back

David Deutsch, following Popper, argues that knowledge grows by conjecture and criticism. An explanation cannot be poured into a learner. The learner has to guess at it, say the guess out loud and find out where it breaks.

So the instruction I give the tutor is: "Ask them to put the idea in their own words, or to say what they'd criticise." Your answer becomes the evidence in the knowledge graph. Uploading a paper or having it read to you writes nothing.

ChatGPT's advantages

ChatGPT does far more than tutor. It writes and runs code and makes images, and Understand does neither.

The older Advanced voice on iOS and Android takes live video and screen sharing, so you can point your phone at a circuit or a page of handwritten algebra. Understand hears you and sees nothing.

ChatGPT has an Android app. Understand runs on the web and on iOS through TestFlight.

Understand is new and has the bugs of a new product.

Understand is free for now. Voice calls cost money to run, so that will not last.

Gemini and Claude

Guided Learning in Gemini launched on August 6, 2025. Google describes "probing and open-ended questions" and answers with "images, diagrams, videos and interactive quizzes". Its help page lists no paid plan as a requirement and shows file uploads. Neither page describes any record of your progress between sessions. Google AI Pro is $19.99 a month. For visual subjects, Gemini's diagrams and videos beat Understand's ASCII board.

Gemini Live is the voice product. Google's help page calls it free and it accepts your camera and your screen. I found no statement from Google on whether Guided Learning runs inside Live.

NotebookLM is now Gemini Notebook. Google renamed it on July 16, 2026 and says more than 30 million people use it. It answers only from the sources you give it and turns them into audio and video summaries. If you have forty PDFs for an exam, it is the best tool on this page. It keeps no model of you.

Claude had a Learning option in its style menu, which Engadget reported opening to all users in August 2025 after starting in Claude for Education. It questioned you before it answered. Anthropic's help article on styles returned a 404 when I checked today, and I could not confirm the option still exists. Voice mode is a beta on every plan, Free included, and counts against your normal usage limits. Pro is $20 a month. Anthropic documents no learner model either.

Mastery systems: ALEKS and Math Academy

ALEKS does model what you know. It is built on Knowledge Space Theory, developed by Jean-Claude Falmagne and Jean-Paul Doignon. Algebra 1 is roughly 350 concepts, which gives millions of possible knowledge states. ALEKS says it locates yours in 25 to 30 questions. It covers math and chemistry and costs $19.95 a month, or $179.95 for twelve.

Math Academy starts with a diagnostic of 30 to 45 minutes, builds your "individual knowledge graph including levels of mastery", and schedules reviews by spaced repetition. It has a Mathematical Foundations series for adults and a Mathematics for Machine Learning course. It costs $49 a month.

If you want to be able to do math, use Math Academy over Understand. Skill at math comes from solving hundreds of graded problems on a schedule, and Understand has no problem sets and no spaced repetition.

ALEKS and Math Academy each work in a fixed domain that experts mapped by hand, and you type your answers. Neither can teach you monetary policy or the paper you saved this morning.

Tutors for school-age students

Khanmigo costs $4 a month or $44 a year and is free for teachers. You must live in the United States with a US billing address and be 18 to sign up; a parent can add up to ten children. It guides students toward an answer and withholds the answer itself. It reads its replies aloud and takes dictation. At that price, tied to Khan Academy's courses, it is the obvious choice for a US high schooler.

Aristotle is the closest thing to Understand in design, aimed at a different age. It is voice-first: students "speak out loud, listen live, and can be interrupted anytime". Its site says it "remembers every session" and that "we break all subjects down into granular skills, then track mistakes and mastery on each one". It serves grades 6 to 12, sends parents a summary after each session, and charges $49 a month for eight sessions or $199 for unlimited, after three free one-hour sessions. It raised a $5 million seed led by True Ventures on September 16, 2026. The site does not say whether a student can read or correct what it tracks.

Synthesis Tutor "covers elementary math for ages 5-11". Its page lists $35 a month against a struck-through $45, or $300 a year.

Brilliant's Koji lives inside Brilliant's courses. It sees the interactive problem you are on, draws on it, and speaks in ElevenLabs voices. Free users get a limited preview and Premium subscribers get unlimited use. Brilliant's help pages gave me no Premium price.

Tools that study a file or generate a course

YouLearn describes itself as "an AI tutor made for you" that chats with "your YouTube video, PDF, slides, websites, files and lectures". Its free plan allows three uploads and five chat messages a day, and Pro is $20 a month or $12 billed yearly. I tested the free tier and wrote it up in my YouLearn review.

Oboe comes from Nir Zicherman and Michael Mignano, who founded Anchor. It generates a course from a prompt, with chapters, quizzes, flashcards and a podcast version. Its homepage now calls it "chat that actually teaches you". TechCrunch reported on December 10, 2025 that course generation is free, Plus is $15 a month and Pro is $40. Oboe's own pricing page returned a 404 today, and I found no mention of uploading your own files.

Language tutors

Speak and Duolingo Max teach languages through spoken conversation. I left them out because practising a language is a different problem from understanding an idea.

Picking one

If you already pay for ChatGPT Plus and want something explained tonight, use Study Mode or voice mode and accept that it knows little about last week.

Math Academy is the answer for anyone who wants to get good at math, and Gemini Notebook for anyone facing an exam with a pile of documents.

For a child in a US school, Khanmigo at $4 is hard to argue with. Aristotle suits a teenager who would rather talk than type, if you can pay $49.

I build Understand for adults who learn by talking, whose reading list keeps growing, and who want the tutor to know next month what they understood this month.

Questions people ask

Is ChatGPT a good tutor?

Yes, for a single session. Study Mode asks before it tells, and Live voice lets you interrupt mid-sentence. OpenAI documents no tracking of what you have mastered, so each new chat depends on whatever its memory happened to keep.

What is the best AI tutor for adults?

For math, Math Academy. For studying your own documents, Gemini Notebook. For learning any subject by voice with a record of what you have understood, I think Understand, and I am biased.

Is there a free AI tutor?

Yes. ChatGPT Study Mode and Gemini Guided Learning are both on free plans with usage limits. Understand is free for now.