Comprehension means making meaning of what is read or getting meaning out of written text.

Without appropriate skills in comprehension, students lack the ability to understand what they read.  Good comprehension skills support reading effectiveness and enjoyment.  Students with adequate comprehension skills use their background knowledge to understand information, make predictions, summarize, infer, monitor their reading, and reflect upon what they have read.

https://www.readingrockets.org/article/what-research-tells-us-about-reading-comprehension-and-comprehension-instruction

Comprehension is typically assessed by having the student to read material and then answer questions about what  was read.  Explicit questions ask specifically about information presented in text.  Inferential questions ask about information that was implied in the text.  Comprehension could also be measured by asking the student to orally retell what was read or summarize the main idea.  A "cloze" activity, where words are omitted from a passage and the student has to supply or identify the word that makes sense, is also a way to measure comprehension. 

Informal Reading Inventories (IRI) are one way to measure reading comprehension.

https://sedl.org/reading/framework/assessment.html#:~:text=The%20most%20common%20reading%20comprehension,often%20these%20are%20called%20IRIs)

Maze 2nd (Student)     Maze 3rd (Student)     

Maze 2nd (Teacher)       Maze 3rd (Teacher)     

Maze 4th (Student) Maze 5th (Student)    

Maze 4th (Teacher) Maze 5th (Teacher)

Maze 6th (Student)        Maze 7th (Student) Maze 8th (Student)

Maze 6th (Teacher)        Maze 7th (Teacher) Maze 8th (Teacher)