MERLOT
MERLOT (Multimedia Educational Resource for Learning and Online Teaching) is a catalogue of vetted teaching materials rather than a dataset you download. Curators and an international community of educators review and index tens of thousands of online learning objects, lessons, simulations, and open textbooks across every academic discipline, layering peer reviews, ratings, and member-built collections on top.
The key thing to grasp is that MERLOT mostly points elsewhere. Each catalogue entry is a description and a link out to material that lives on someone else's site. You browse and search through the web interface, and there is no bulk export or open API for the underlying content, so building a corpus from it means following the links and retrieving each target yourself.
For RAG, MERLOT earns its place as a discovery layer: a way to find high-quality, human-reviewed educational content on a topic before you commit to ingesting anything. It suits teams building tutoring or curriculum assistants who want curated, reviewed material rather than whatever a raw web crawl happens to turn up.
The caveats are those of any pointer catalogue. Because the resources are hosted externally, licence terms vary from one item to the next, so you must check the terms on each resource before reusing it rather than assuming a single blanket licence. Links rot over time, and what you find at the far end (HTML, PDF, an interactive applet) is inconsistent, so extraction takes real work.
It sits alongside OER Commons and the Mason OER Metafinder in the open educational resources discovery toolkit. Use MERLOT and those tools to locate content, then handle the ingestion, extraction, and per-item licence checking yourself.
Related sources
CASE Network (1EdTech)
A public registry of machine-readable learning-standard frameworks from all 50 US states and other issuing agencies, run by 1EdTech in the CASE JSON format. The digitally referenceable spine of what to teach, at which level and in what order, rather than the teaching content itself.
CK-12 Foundation
Free K-12 library of customisable FlexBook textbooks, strong in maths and science, with adaptive practice, interactive simulations and study guides, organised by grade level and aligned to state standards. Non-commercial licence.
Common Core State Standards
The US Common Core State Standards for English language arts and mathematics, defined grade by grade from kindergarten to grade twelve. A widely adopted curriculum framework, available in machine-readable form through ASN and CASE.
Khan Academy
A free nonprofit learning platform organised as a subject-to-skill knowledge tree across maths, science, economics and the humanities, from primary through early college. Videos, articles and mastery-based exercises, but non-commercial licensing and no public data API.