The most common and most likely answer to this crossword clue is the 7 letter word SCHOOLS
I've seen this crossword clue in The Guardian
S
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Buddy explains!
The straight part
We know that "Teaches/groups" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case teaches/groups = schools.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SCHOOLS mean?
SCHOOLS noun- (collective) A group of fish or a group of marine mammals such as porpoises, dolphins, or whales.
- A multitude.
- (of fish) To form into, or travel in a school.
- An institution dedicated to teaching and learning; an educational institution.
- An educational institution providing primary and secondary education, prior to tertiary education (college or university).
- At Eton College, a period or session of teaching.
- Within a larger educational institution, an organizational unit, such as a department or institute, which is dedicated to a specific subject area.
- An art movement, a community of artists.
- (considered collectively) The followers of a particular doctrine; a particular way of thinking or particular doctrine; a school of thought.
- The time during which classes are attended or in session in an educational institution.
- The room or hall in English universities where the examinations for degrees and honours are held.
- The canons, precepts, or body of opinion or practice, sanctioned by the authority of a particular class or age.
- An establishment offering specialized instruction, as for driving, cooking, typing, coding, etc.
- To educate, teach, or train (often, but not necessarily, in a school).
- To defeat emphatically, to teach an opponent a harsh lesson.
- To control, or compose, one's expression.