The teacher reads the passage that is dictated to students.
The students write at their teacher's dictation.
This means "take dictation".
memory is the power of keeping facts in the conscious mind and of being able to call (the piece passage) back at will.
To commit something(ie.200 words piece of passage) to memory means to learn it by heart and hence dictation from memory without referring to passage notes or from the teacher's speaking and listening, reading and writing. The writing would be done by the memory power in each individual student..
The student of blessed memory has better "memory dictation" result.