The most common and most likely answer to this crossword clue is the 6 letter word SCOPES
I've seen this crossword clue in The Daily Telegraph
S
C
O
P
E
S
Buddy explains!
The straight part
We know that "Famous US science teacher/optical instruments" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case famous us science teacher/optical instruments = scopes.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 SCOPES mean?
SCOPES noun- The breadth, depth or reach of a subject; a domain.
- A device used in aiming a projectile, through which the person aiming looks at the intended target.
- Opportunity; broad range; degree of freedom.
- The region of program source code in which a given identifier is meaningful, or a given object can be accessed.
- The shortest sub-wff of which a given instance of a logical connective is a part.
- The region of an utterance to which some modifying element applies.
- A periscope, telescope, microscope or oscilloscope.
- Any medical procedure that ends in the suffix -scopy, such as endoscopy, colonoscopy, bronchoscopy, etc.
- To perform a cursory investigation of; scope out.
- To perform any medical procedure that ends in the suffix -scopy, such as endoscopy, colonoscopy, bronchoscopy, etc.
- To limit (an object or variable) to a certain region of program source code.
- To examine under a microscope.
- To observe a bird using a spotting scope.
- A bundle, as of twigs.