Things associated with effective schools: one study [only] says ...

Things that predict effective schools: frequent teacher feedback, the use of data on students to guide instruction, frequent tutoring sessions [4x a week+], higher number of instructional hours, and having high expectations.
Things that don't: class size, per-pupil expenditure, teacher certification, teacher training.
Just one article, but thought-provoking:

http://www.nyccharterschools.org/sites/default/files/resources/effective_schools_fryer.pdf