I’m occasionally asked about different types of language learning materials, such as what the difference is between a “sketch grammar”, a “textbook” and a “learner’s guide”. I think the difference is one of audience/function more than anything else – it’s not necessarily the information that goes into them.
A sketch grammar is written for linguists. It’s like a reference grammar but it’s shorter. It contains basic information about phonology, syntax, and morphology (and maybe a text or two) but not too much else. Most of the Lincom Languages of the World/Materials series are sketch grammars. Such books aren’t usually very easy to use to learn a language from. They usually don’t contain a wordlist (or if they do, it won’t necessarily contain helpful vocabulary), they aren’t laid out in a pedagogically friendly way and there’s usually no attempt to explain technical terms.
A textbook is primarily written for school use. There is an implicit assumption that there will be a teacher (or that the student will have somewhere to go for help). They are usually set out by subject theme rather than by linguistic concept (e.g. a chapter heading is more likely to be “going to the cinema”, than “adjectives”). They often avoid talking about grammatical terminology at all.* Textbooks usually don’t teach phonology overtly either (although they will usually contain information about the sounds of the language).
A learner’s guide is a bit of a catch-all. The audience isn’t assumed to be school kids (that is, it’s not assumed that the language will be learned in a classroom situation). The learner’s guides are often written by linguists and assume a sketch grammar model, but they contain less linguistic terminology (or they explain the terms they use).
*<rant>: I have never understood this. Why should a concept be any easier to master if it’s not identified or named?? </rant>