The main criteria in education is assessment, as teachers need to know how much students have learnt in the classroom, whether or not they are ready for following chapter of education and, if so, what aspect is most suitable for them.
(I'd appreciate it if you help me with this sentence to keep it as "one sentence" with correct punctuation and grammar)
The word "criteria" does not feel like quite the right word in this sentence. A few ideas:
"Assessment is an essential component of education..."
"An essential component of education is assessment..."
"A crucial _________ in education is assessment...."
And maybe "aspect" could be replaced by another word like "opportunities" or "options" or "programs" or "pathways" or "courses" or "curriculum"? The reason I hesitate to use "aspect" is that although education has many aspects, it doesn't seem like we CHOOSE "aspects" for each individual student.