EF is slow, IMX. But I think it mainly has to do with the fact that it's an ORM, and since the application un-marshals to objects and marshals back to the data store more or less one object at a time, you lose set-based operations. If you're interacting with a lot of discrete, unrelated objects, that gets really inefficient. You can easily end up with the dreaded "row by agonizing row" pattern:
UPDATE Student SET Grade = '04' WHERE StudentId = '12345'
UPDATE Student SET Grade = '04' WHERE StudentId = '12346'
UPDATE Student SET Grade = '04' WHERE StudentId = '12347'
UPDATE Student SET Grade = '04' WHERE StudentId = '12348'
.
.
.
.
UPDATE Student SET Grade = '04' WHERE StudentId = '12349'
Instead of:
UPDATE Student SET Grade = '04' WHERE StudentId IN ('12345','12346','12347','12348', ...., '12349')
