SJ's? I know ISTJ's do well in school, but I'd take an INTJ in the classroom over an ISTJ any day of the week. Especially graduate level stuff - Master's, Ph.D., etc.
If you're talking something like accounting, then yeah, ISTJ's. But, the deeper you go into a subject, the ISTJ's will lose interest. I know 2 ISTJ's who did awesome in high school and college (accounting; engineering), but when you started talking about the Master's type material - the deeper understanding of the subject, they checked out. They didn't want anything to do with it. When you get into more complex subjects like Physics, neuroscience, and medicine, stuff like that, SJ would not be the *best in the classroom*. Also, stuff like languages and humanities would, all things equal, tend to be more fit for some of the NF types. It really just depends on what types of skills are required for each subject.